[Xen-devel,v4,1/2] xen: Switch parameter in get_page_from_gfn to use typesafe gfn

Message ID 20190819142651.11058-2-julien.grall@arm.com
State New
Headers show
Series
  • More typesafe conversion of common interface
Related show

Commit Message

Julien Grall Aug. 19, 2019, 2:26 p.m.
No functional change intended.

Only reasonable clean-ups are done in this patch. The rest will use _gfn
for the time being.

The code in get_page_from_gfn is slightly reworked to also handle a bad
behavior because it is not safe to use mfn_to_page(...) because
mfn_valid(...) succeeds.

Signed-off-by: Julien Grall <julien.grall@arm.com>

---
    Changes in v4:
        - Drop all the reviewed-by/acked-by as the last version was
        sent nearly 9 months ago.
        - Rework the change in x86 version get_page_from_gfn
        - s/%#PRI_/%PRI_/

    Changes in v3:
        - Add Jan's acked-by

    Changes in v2:
        - Remove >> PAGE_SHIFT in svm code
        - Fix typo in the e-mail address
        - Small NITs
---
 xen/arch/arm/guestcopy.c             |  2 +-
 xen/arch/arm/mm.c                    |  2 +-
 xen/arch/x86/cpu/vpmu.c              |  2 +-
 xen/arch/x86/domctl.c                |  6 +++---
 xen/arch/x86/hvm/dm.c                |  2 +-
 xen/arch/x86/hvm/domain.c            |  6 ++++--
 xen/arch/x86/hvm/hvm.c               |  9 +++++----
 xen/arch/x86/hvm/svm/svm.c           |  8 ++++----
 xen/arch/x86/hvm/viridian/viridian.c | 16 ++++++++--------
 xen/arch/x86/hvm/vmx/vmx.c           |  4 ++--
 xen/arch/x86/hvm/vmx/vvmx.c          | 12 ++++++------
 xen/arch/x86/mm.c                    | 24 ++++++++++++++----------
 xen/arch/x86/mm/p2m.c                |  2 +-
 xen/arch/x86/mm/shadow/hvm.c         |  6 +++---
 xen/arch/x86/physdev.c               |  3 ++-
 xen/arch/x86/pv/descriptor-tables.c  |  4 ++--
 xen/arch/x86/pv/emul-priv-op.c       |  6 +++---
 xen/arch/x86/pv/mm.c                 |  2 +-
 xen/arch/x86/traps.c                 | 11 ++++++-----
 xen/common/domain.c                  |  2 +-
 xen/common/event_fifo.c              | 12 ++++++------
 xen/common/memory.c                  |  4 ++--
 xen/include/asm-arm/p2m.h            |  6 +++---
 xen/include/asm-x86/p2m.h            | 16 ++++++++++++----
 24 files changed, 92 insertions(+), 75 deletions(-)

Comments

Paul Durrant Aug. 20, 2019, 8:15 a.m. | #1
> -----Original Message-----
> From: Julien Grall <julien.grall@arm.com>
> Sent: 19 August 2019 15:27
> To: xen-devel@lists.xenproject.org
> Cc: Julien Grall <julien.grall@arm.com>; Stefano Stabellini <sstabellini@kernel.org>; Volodymyr
> Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper <Andrew.Cooper3@citrix.com>; George Dunlap
> <George.Dunlap@citrix.com>; Ian Jackson <Ian.Jackson@citrix.com>; Jan Beulich <jbeulich@suse.com>;
> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Tim (Xen.org) <tim@xen.org>; Wei Liu <wl@xen.org>;
> Roger Pau Monne <roger.pau@citrix.com>; Boris Ostrovsky <boris.ostrovsky@oracle.com>; Suravee
> Suthikulpanit <suravee.suthikulpanit@amd.com>; Brian Woods <brian.woods@amd.com>; Paul Durrant
> <Paul.Durrant@citrix.com>; Jun Nakajima <jun.nakajima@intel.com>; Kevin Tian <kevin.tian@intel.com>
> Subject: [PATCH v4 1/2] xen: Switch parameter in get_page_from_gfn to use typesafe gfn
> 
> No functional change intended.
> 
> Only reasonable clean-ups are done in this patch. The rest will use _gfn
> for the time being.
> 
> The code in get_page_from_gfn is slightly reworked to also handle a bad
> behavior because it is not safe to use mfn_to_page(...) because
> mfn_valid(...) succeeds.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>

Reviewed-by: Paul Durrant <paul.durrant@citrix.com>

... with a few suggestions below ...

[snip]
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 029eea3b85..236bd6ed38 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2168,7 +2168,7 @@ int hvm_set_cr0(unsigned long value, bool may_defer)
>  {
>      struct vcpu *v = current;
>      struct domain *d = v->domain;
> -    unsigned long gfn, old_value = v->arch.hvm.guest_cr[0];
> +    unsigned long old_value = v->arch.hvm.guest_cr[0];
>      struct page_info *page;
> 
>      HVM_DBG_LOG(DBG_LEVEL_VMMU, "Update CR0 value = %lx", value);
> @@ -2223,7 +2223,8 @@ int hvm_set_cr0(unsigned long value, bool may_defer)
>          if ( !paging_mode_hap(d) )
>          {
>              /* The guest CR3 must be pointing to the guest physical. */
> -            gfn = v->arch.hvm.guest_cr[3] >> PAGE_SHIFT;
> +            gfn_t gfn = gaddr_to_gfn(v->arch.hvm.guest_cr[3]);
> +
>              page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
>              if ( !page )
>              {
> @@ -2315,7 +2316,7 @@ int hvm_set_cr3(unsigned long value, bool may_defer)
>      {
>          /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
>          HVM_DBG_LOG(DBG_LEVEL_VMMU, "CR3 value = %lx", value);
> -        page = get_page_from_gfn(v->domain, value >> PAGE_SHIFT,
> +        page = get_page_from_gfn(v->domain, gaddr_to_gfn(value),
>                                   NULL, P2M_ALLOC);

I think you can reduce the scope of 'page' above in the same way you did with 'gfn' above

>          if ( !page )
>              goto bad_cr3;

[snip]
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 0060310d74..38bdef0862 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -674,7 +674,7 @@ static int vmx_restore_cr0_cr3(
>      {
>          if ( cr0 & X86_CR0_PG )
>          {
> -            page = get_page_from_gfn(v->domain, cr3 >> PAGE_SHIFT,
> +            page = get_page_from_gfn(v->domain, gaddr_to_gfn(cr3),
>                                       NULL, P2M_ALLOC);

Here also you can reduce the scope of 'page' (although only into the scope just outside the 'if')

>              if ( !page )
>              {

[snip]
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 7531406543..f8e2b6f921 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -2083,7 +2083,7 @@ static int mod_l1_entry(l1_pgentry_t *pl1e, l1_pgentry_t nl1e,
>              p2m_query_t q = l1e_get_flags(nl1e) & _PAGE_RW ?
>                              P2M_ALLOC | P2M_UNSHARE : P2M_ALLOC;
> 
> -            page = get_page_from_gfn(pg_dom, l1e_get_pfn(nl1e), &p2mt, q);
> +            page = get_page_from_gfn(pg_dom, _gfn(l1e_get_pfn(nl1e)), &p2mt, q);
> 

'l1e_get_pfn(nl1e)' is repeated 3 times within this scope AFAICT so probably worth a local variable while you're in the neighbourhood, to reduce verbosity.

>              if ( p2m_is_paged(p2mt) )
>              {

[snip]
> diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
> index 3a3c15890b..4f3f438614 100644
> --- a/xen/arch/x86/physdev.c
> +++ b/xen/arch/x86/physdev.c
> @@ -229,7 +229,8 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>              break;
> 
>          ret = -EINVAL;
> -        page = get_page_from_gfn(current->domain, info.gmfn, NULL, P2M_ALLOC);
> +        page = get_page_from_gfn(current->domain, _gfn(info.gmfn),
> +                                 NULL, P2M_ALLOC);

'currd' has actually been defined at the top of the function so if you lose the 'current->domain' you can re-flow this back onto one line I think.

>          if ( !page )
>              break;
>          if ( !get_page_type(page, PGT_writable_page) )
Julien Grall Aug. 21, 2019, 5:52 p.m. | #2
Hi Paul,

Thank you for the review,

On 20/08/2019 09:15, Paul Durrant wrote:
>> -----Original Message-----
>> From: Julien Grall <julien.grall@arm.com>
>> Sent: 19 August 2019 15:27
>> To: xen-devel@lists.xenproject.org
>> Cc: Julien Grall <julien.grall@arm.com>; Stefano Stabellini <sstabellini@kernel.org>; Volodymyr
>> Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper <Andrew.Cooper3@citrix.com>; George Dunlap
>> <George.Dunlap@citrix.com>; Ian Jackson <Ian.Jackson@citrix.com>; Jan Beulich <jbeulich@suse.com>;
>> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; Tim (Xen.org) <tim@xen.org>; Wei Liu <wl@xen.org>;
>> Roger Pau Monne <roger.pau@citrix.com>; Boris Ostrovsky <boris.ostrovsky@oracle.com>; Suravee
>> Suthikulpanit <suravee.suthikulpanit@amd.com>; Brian Woods <brian.woods@amd.com>; Paul Durrant
>> <Paul.Durrant@citrix.com>; Jun Nakajima <jun.nakajima@intel.com>; Kevin Tian <kevin.tian@intel.com>
>> Subject: [PATCH v4 1/2] xen: Switch parameter in get_page_from_gfn to use typesafe gfn
>>
>> No functional change intended.
>>
>> Only reasonable clean-ups are done in this patch. The rest will use _gfn
>> for the time being.
>>
>> The code in get_page_from_gfn is slightly reworked to also handle a bad
>> behavior because it is not safe to use mfn_to_page(...) because
>> mfn_valid(...) succeeds.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
> 
> Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
> 
> ... with a few suggestions below ...
> 
> [snip]
>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
>> index 029eea3b85..236bd6ed38 100644
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -2168,7 +2168,7 @@ int hvm_set_cr0(unsigned long value, bool may_defer)
>>   {
>>       struct vcpu *v = current;
>>       struct domain *d = v->domain;
>> -    unsigned long gfn, old_value = v->arch.hvm.guest_cr[0];
>> +    unsigned long old_value = v->arch.hvm.guest_cr[0];
>>       struct page_info *page;
>>
>>       HVM_DBG_LOG(DBG_LEVEL_VMMU, "Update CR0 value = %lx", value);
>> @@ -2223,7 +2223,8 @@ int hvm_set_cr0(unsigned long value, bool may_defer)
>>           if ( !paging_mode_hap(d) )
>>           {
>>               /* The guest CR3 must be pointing to the guest physical. */
>> -            gfn = v->arch.hvm.guest_cr[3] >> PAGE_SHIFT;
>> +            gfn_t gfn = gaddr_to_gfn(v->arch.hvm.guest_cr[3]);
>> +
>>               page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
>>               if ( !page )
>>               {
>> @@ -2315,7 +2316,7 @@ int hvm_set_cr3(unsigned long value, bool may_defer)
>>       {
>>           /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
>>           HVM_DBG_LOG(DBG_LEVEL_VMMU, "CR3 value = %lx", value);
>> -        page = get_page_from_gfn(v->domain, value >> PAGE_SHIFT,
>> +        page = get_page_from_gfn(v->domain, gaddr_to_gfn(value),
>>                                    NULL, P2M_ALLOC);
> 
> I think you can reduce the scope of 'page' above in the same way you did with 'gfn' above

For this one and ...

> 
>>           if ( !page )
>>               goto bad_cr3;
> 
> [snip]
>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>> index 0060310d74..38bdef0862 100644
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -674,7 +674,7 @@ static int vmx_restore_cr0_cr3(
>>       {
>>           if ( cr0 & X86_CR0_PG )
>>           {
>> -            page = get_page_from_gfn(v->domain, cr3 >> PAGE_SHIFT,
>> +            page = get_page_from_gfn(v->domain, gaddr_to_gfn(cr3),
>>                                        NULL, P2M_ALLOC);
> 
> Here also you can reduce the scope of 'page' (although only into the scope just outside the 'if')

... this one, we don't change the type of the variable so I don't feel such 
clean-ups belong to this patch.

> 
>>               if ( !page )
>>               {
> 
> [snip]
>> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
>> index 7531406543..f8e2b6f921 100644
>> --- a/xen/arch/x86/mm.c
>> +++ b/xen/arch/x86/mm.c
>> @@ -2083,7 +2083,7 @@ static int mod_l1_entry(l1_pgentry_t *pl1e, l1_pgentry_t nl1e,
>>               p2m_query_t q = l1e_get_flags(nl1e) & _PAGE_RW ?
>>                               P2M_ALLOC | P2M_UNSHARE : P2M_ALLOC;
>>
>> -            page = get_page_from_gfn(pg_dom, l1e_get_pfn(nl1e), &p2mt, q);
>> +            page = get_page_from_gfn(pg_dom, _gfn(l1e_get_pfn(nl1e)), &p2mt, q);
>>
> 
> 'l1e_get_pfn(nl1e)' is repeated 3 times within this scope AFAICT so probably worth a local variable while you're in the neighbourhood, to reduce verbosity.

I can only find 2 use of l1e_get_pfn within mod_l1_entry. But then, this sort of 
clean-up should be in there own patch.

But I will leave that to the x86 folks as I don't want to be roped in endless 
clean-up. I know there will be more ;).

> 
>>               if ( p2m_is_paged(p2mt) )
>>               {
> 
> [snip]
>> diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
>> index 3a3c15890b..4f3f438614 100644
>> --- a/xen/arch/x86/physdev.c
>> +++ b/xen/arch/x86/physdev.c
>> @@ -229,7 +229,8 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>>               break;
>>
>>           ret = -EINVAL;
>> -        page = get_page_from_gfn(current->domain, info.gmfn, NULL, P2M_ALLOC);
>> +        page = get_page_from_gfn(current->domain, _gfn(info.gmfn),
>> +                                 NULL, P2M_ALLOC);
> 
> 'currd' has actually been defined at the top of the function so if you lose the 'current->domain' you can re-flow this back onto one line I think.

Sounds reasonable, but there are 3 more characters than the normal, so it will 
still have to live on 2 lines :(.

Cheers,
Andrew Cooper Aug. 23, 2019, 2:07 p.m. | #3
On 19/08/2019 15:26, Julien Grall wrote:
> No functional change intended.
>
> Only reasonable clean-ups are done in this patch. The rest will use _gfn
> for the time being.
>
> The code in get_page_from_gfn is slightly reworked to also handle a bad
> behavior because it is not safe to use mfn_to_page(...) because
> mfn_valid(...) succeeds.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>
>
> ---
>     Changes in v4:
>         - Drop all the reviewed-by/acked-by as the last version was
>         sent nearly 9 months ago.
>         - Rework the change in x86 version get_page_from_gfn
>         - s/%#PRI_/%PRI_/

This doesn't appear to have happened everywhere.  There are two viridian
examples and one in guest_wrmsr_xen().  Can be fixed on commit.

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Jan Beulich Aug. 29, 2019, 3:41 p.m. | #4
On 19.08.2019 16:26, Julien Grall wrote:
> No functional change intended.
> 
> Only reasonable clean-ups are done in this patch. The rest will use _gfn
> for the time being.
> 
> The code in get_page_from_gfn is slightly reworked to also handle a bad
> behavior because it is not safe to use mfn_to_page(...) because
> mfn_valid(...) succeeds.

I guess the 2nd "because" is meant to be "before", but even then I
don't think I can easily agree: mfn_to_page() is just calculations,
no dereference.

> --- a/xen/arch/x86/hvm/domain.c
> +++ b/xen/arch/x86/hvm/domain.c
> @@ -296,8 +296,10 @@ int arch_set_info_hvm_guest(struct vcpu *v, const vcpu_hvm_context_t *ctx)
>      if ( hvm_paging_enabled(v) && !paging_mode_hap(v->domain) )
>      {
>          /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
> -        struct page_info *page = get_page_from_gfn(v->domain,
> -                                 v->arch.hvm.guest_cr[3] >> PAGE_SHIFT,
> +        struct page_info *page;
> +
> +        page = get_page_from_gfn(v->domain,
> +                                 gaddr_to_gfn(v->arch.hvm.guest_cr[3]),
>                                   NULL, P2M_ALLOC);

Iirc I've said so before: I consider use of gaddr_to_gfn() here more
misleading than a plain shift by PAGE_SHIFT. Neither is really correct,
but in no event does CR3 as a whole hold an address. (Same elsewhere
then, and sadly in quite a few places.)

> --- a/xen/common/event_fifo.c
> +++ b/xen/common/event_fifo.c
> @@ -361,7 +361,7 @@ static const struct evtchn_port_ops evtchn_port_ops_fifo =
>      .print_state   = evtchn_fifo_print_state,
>  };
>  
> -static int map_guest_page(struct domain *d, uint64_t gfn, void **virt)
> +static int map_guest_page(struct domain *d, gfn_t gfn, void **virt)
>  {
>      struct page_info *p;
>  
> @@ -422,7 +422,7 @@ static int setup_control_block(struct vcpu *v)
>      return 0;
>  }
>  
> -static int map_control_block(struct vcpu *v, uint64_t gfn, uint32_t offset)
> +static int map_control_block(struct vcpu *v, gfn_t gfn, uint32_t offset)
>  {
>      void *virt;
>      unsigned int i;

Just as a remark (no action expected) - this makes a truncation issue
pretty apparent: On 32-bit platforms the upper 32 bits of a passed in
GFN get ignored. Correct (imo) behavior would be to reject the upper
bits being non-zero.

Jan
Julien Grall Aug. 29, 2019, 5:36 p.m. | #5
Hi,

On 29/08/2019 17:41, Jan Beulich wrote:
> On 19.08.2019 16:26, Julien Grall wrote:

>> No functional change intended.

>>

>> Only reasonable clean-ups are done in this patch. The rest will use _gfn

>> for the time being.

>>

>> The code in get_page_from_gfn is slightly reworked to also handle a bad

>> behavior because it is not safe to use mfn_to_page(...) because

>> mfn_valid(...) succeeds.

> 

> I guess the 2nd "because" is meant to be "before", but even then I

> don't think I can easily agree: mfn_to_page() is just calculations,

> no dereference.


Regardless the s/because/before/. Do you disagree on the wording or the 
change? If the former, I just paraphrased what Andrew wrote in the 
previous version:

"This unfortunately propagates some bad behaviour, because it is not 
safe to use mfn_to_page(mfn); before mfn_valid(mfn) succeeds.  (In 
practice it works because mfn_to_page() is just pointer arithmetic.)"

This is x86 code, so please agree with Andrew on the approach/wording.

> 

>> --- a/xen/arch/x86/hvm/domain.c

>> +++ b/xen/arch/x86/hvm/domain.c

>> @@ -296,8 +296,10 @@ int arch_set_info_hvm_guest(struct vcpu *v, const vcpu_hvm_context_t *ctx)

>>       if ( hvm_paging_enabled(v) && !paging_mode_hap(v->domain) )

>>       {

>>           /* Shadow-mode CR3 change. Check PDBR and update refcounts. */

>> -        struct page_info *page = get_page_from_gfn(v->domain,

>> -                                 v->arch.hvm.guest_cr[3] >> PAGE_SHIFT,

>> +        struct page_info *page;

>> +

>> +        page = get_page_from_gfn(v->domain,

>> +                                 gaddr_to_gfn(v->arch.hvm.guest_cr[3]),

>>                                    NULL, P2M_ALLOC);

> 

> Iirc I've said so before: I consider use of gaddr_to_gfn() here more

> misleading than a plain shift by PAGE_SHIFT. Neither is really correct,

> but in no event does CR3 as a whole hold an address. (Same elsewhere

> then, and sadly in quite a few places.)


Well, this code has not changed since v3 and you acked it... I only 
dropped the ack here because the previous version was sent 9 months ago. 
I also can't see such comment made on any version of this series.

Anyway, I am more than happy to switch to _gfn((v->arch.hvm.guest_cr[3] 
 >> PAGE_SHIFT)) if you prefer it.


> 

>> --- a/xen/common/event_fifo.c

>> +++ b/xen/common/event_fifo.c

>> @@ -361,7 +361,7 @@ static const struct evtchn_port_ops evtchn_port_ops_fifo =

>>       .print_state   = evtchn_fifo_print_state,

>>   };

>>   

>> -static int map_guest_page(struct domain *d, uint64_t gfn, void **virt)

>> +static int map_guest_page(struct domain *d, gfn_t gfn, void **virt)

>>   {

>>       struct page_info *p;

>>   

>> @@ -422,7 +422,7 @@ static int setup_control_block(struct vcpu *v)

>>       return 0;

>>   }

>>   

>> -static int map_control_block(struct vcpu *v, uint64_t gfn, uint32_t offset)

>> +static int map_control_block(struct vcpu *v, gfn_t gfn, uint32_t offset)

>>   {

>>       void *virt;

>>       unsigned int i;

> 

> Just as a remark (no action expected) - this makes a truncation issue

> pretty apparent: On 32-bit platforms the upper 32 bits of a passed in

> GFN get ignored. Correct (imo) behavior would be to reject the upper

> bits being non-zero.


This is not only here but on pretty much all the hypercalls taking a gfn 
(on Arm it is 64-bit regardless the bitness).

I agree this is not nice, but I am afraid this is likely another can of 
worm that I am not to open it yet.

Cheers,

-- 
Julien Grall
Jan Beulich Aug. 30, 2019, 7:20 a.m. | #6
On 29.08.2019 19:36, Julien Grall wrote:
> On 29/08/2019 17:41, Jan Beulich wrote:
>> On 19.08.2019 16:26, Julien Grall wrote:
>>> No functional change intended.
>>>
>>> Only reasonable clean-ups are done in this patch. The rest will use _gfn
>>> for the time being.
>>>
>>> The code in get_page_from_gfn is slightly reworked to also handle a bad
>>> behavior because it is not safe to use mfn_to_page(...) because
>>> mfn_valid(...) succeeds.
>>
>> I guess the 2nd "because" is meant to be "before", but even then I
>> don't think I can easily agree: mfn_to_page() is just calculations,
>> no dereference.
> 
> Regardless the s/because/before/. Do you disagree on the wording or the 
> change? If the former, I just paraphrased what Andrew wrote in the 
> previous version:
> 
> "This unfortunately propagates some bad behaviour, because it is not 
> safe to use mfn_to_page(mfn); before mfn_valid(mfn) succeeds.  (In 
> practice it works because mfn_to_page() is just pointer arithmetic.)"
> 
> This is x86 code, so please agree with Andrew on the approach/wording.

Andrew - I don't see much point altering the ordering in a mechanical
patch like this one, when there are (presumably) dozens of other places
doing the same. I agree it's a grey area, but I don't think doing the
pointer arithmetic up front can really be called UB in the sense that
it may cause the compiler to mis-optimize things. This is in particular
because we don't declare frame_table[]'s bounds anywhere, so the
compiler has to view this as an array extending all the way up to the
upper address space end.

If we really were concerned, we should go through and change all such
instances.

>>> --- a/xen/arch/x86/hvm/domain.c
>>> +++ b/xen/arch/x86/hvm/domain.c
>>> @@ -296,8 +296,10 @@ int arch_set_info_hvm_guest(struct vcpu *v, const vcpu_hvm_context_t *ctx)
>>>       if ( hvm_paging_enabled(v) && !paging_mode_hap(v->domain) )
>>>       {
>>>           /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
>>> -        struct page_info *page = get_page_from_gfn(v->domain,
>>> -                                 v->arch.hvm.guest_cr[3] >> PAGE_SHIFT,
>>> +        struct page_info *page;
>>> +
>>> +        page = get_page_from_gfn(v->domain,
>>> +                                 gaddr_to_gfn(v->arch.hvm.guest_cr[3]),
>>>                                    NULL, P2M_ALLOC);
>>
>> Iirc I've said so before: I consider use of gaddr_to_gfn() here more
>> misleading than a plain shift by PAGE_SHIFT. Neither is really correct,
>> but in no event does CR3 as a whole hold an address. (Same elsewhere
>> then, and sadly in quite a few places.)
> 
> Well, this code has not changed since v3 and you acked it... I only 
> dropped the ack here because the previous version was sent 9 months ago. 
> I also can't see such comment made on any version of this series.

Well, it may not have been this patch, but I clearly recall pointing
this aspect out before; I think it was even more than once.

> Anyway, I am more than happy to switch to _gfn((v->arch.hvm.guest_cr[3] 
>  >> PAGE_SHIFT)) if you prefer it.

Personally I'd much prefer introducing (and then using)

#define gcr3_to_gfn(cr3) gaddr_to_gfn((cr3) & X86_CR3_ADDR_MASK)

>>> --- a/xen/common/event_fifo.c
>>> +++ b/xen/common/event_fifo.c
>>> @@ -361,7 +361,7 @@ static const struct evtchn_port_ops evtchn_port_ops_fifo =
>>>       .print_state   = evtchn_fifo_print_state,
>>>   };
>>>   
>>> -static int map_guest_page(struct domain *d, uint64_t gfn, void **virt)
>>> +static int map_guest_page(struct domain *d, gfn_t gfn, void **virt)
>>>   {
>>>       struct page_info *p;
>>>   
>>> @@ -422,7 +422,7 @@ static int setup_control_block(struct vcpu *v)
>>>       return 0;
>>>   }
>>>   
>>> -static int map_control_block(struct vcpu *v, uint64_t gfn, uint32_t offset)
>>> +static int map_control_block(struct vcpu *v, gfn_t gfn, uint32_t offset)
>>>   {
>>>       void *virt;
>>>       unsigned int i;
>>
>> Just as a remark (no action expected) - this makes a truncation issue
>> pretty apparent: On 32-bit platforms the upper 32 bits of a passed in
>> GFN get ignored. Correct (imo) behavior would be to reject the upper
>> bits being non-zero.
> 
> This is not only here but on pretty much all the hypercalls taking a gfn 
> (on Arm it is 64-bit regardless the bitness).
> 
> I agree this is not nice, but I am afraid this is likely another can of 
> worm that I am not to open it yet.

Right - hence me saying "no action expected".

Jan

Patch

diff --git a/xen/arch/arm/guestcopy.c b/xen/arch/arm/guestcopy.c
index 7a0f3e9d5f..55892062bb 100644
--- a/xen/arch/arm/guestcopy.c
+++ b/xen/arch/arm/guestcopy.c
@@ -37,7 +37,7 @@  static struct page_info *translate_get_page(copy_info_t info, uint64_t addr,
         return get_page_from_gva(info.gva.v, addr,
                                  write ? GV2M_WRITE : GV2M_READ);
 
-    page = get_page_from_gfn(info.gpa.d, paddr_to_pfn(addr), &p2mt, P2M_ALLOC);
+    page = get_page_from_gfn(info.gpa.d, gaddr_to_gfn(addr), &p2mt, P2M_ALLOC);
 
     if ( !page )
         return NULL;
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index e1cdeaaf2f..e9afd53e69 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1405,7 +1405,7 @@  int xenmem_add_to_physmap_one(
 
         /* Take reference to the foreign domain page.
          * Reference will be released in XENMEM_remove_from_physmap */
-        page = get_page_from_gfn(od, idx, &p2mt, P2M_ALLOC);
+        page = get_page_from_gfn(od, _gfn(idx), &p2mt, P2M_ALLOC);
         if ( !page )
         {
             put_pg_owner(od);
diff --git a/xen/arch/x86/cpu/vpmu.c b/xen/arch/x86/cpu/vpmu.c
index 375599aca5..c5a4c9a603 100644
--- a/xen/arch/x86/cpu/vpmu.c
+++ b/xen/arch/x86/cpu/vpmu.c
@@ -590,7 +590,7 @@  static int pvpmu_init(struct domain *d, xen_pmu_params_t *params)
     struct vcpu *v;
     struct vpmu_struct *vpmu;
     struct page_info *page;
-    uint64_t gfn = params->val;
+    gfn_t gfn = _gfn(params->val);
 
     if ( (params->vcpu >= d->max_vcpus) || (d->vcpu[params->vcpu] == NULL) )
         return -EINVAL;
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 2d45e5b8a8..3ce2dd1463 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -453,7 +453,7 @@  long arch_do_domctl(
                 break;
             }
 
-            page = get_page_from_gfn(d, gfn, &t, P2M_ALLOC);
+            page = get_page_from_gfn(d, _gfn(gfn), &t, P2M_ALLOC);
 
             if ( unlikely(!page) ||
                  unlikely(is_xen_heap_page(page)) )
@@ -503,11 +503,11 @@  long arch_do_domctl(
 
     case XEN_DOMCTL_hypercall_init:
     {
-        unsigned long gmfn = domctl->u.hypercall_init.gmfn;
+        gfn_t gfn = _gfn(domctl->u.hypercall_init.gmfn);
         struct page_info *page;
         void *hypercall_page;
 
-        page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
+        page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
 
         if ( !page || !get_page_type(page, PGT_writable_page) )
         {
diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
index d6d0e8be89..3b3ad27938 100644
--- a/xen/arch/x86/hvm/dm.c
+++ b/xen/arch/x86/hvm/dm.c
@@ -186,7 +186,7 @@  static int modified_memory(struct domain *d,
         {
             struct page_info *page;
 
-            page = get_page_from_gfn(d, pfn, NULL, P2M_UNSHARE);
+            page = get_page_from_gfn(d, _gfn(pfn), NULL, P2M_UNSHARE);
             if ( page )
             {
                 paging_mark_pfn_dirty(d, _pfn(pfn));
diff --git a/xen/arch/x86/hvm/domain.c b/xen/arch/x86/hvm/domain.c
index 5d5a746a25..3c29ff86be 100644
--- a/xen/arch/x86/hvm/domain.c
+++ b/xen/arch/x86/hvm/domain.c
@@ -296,8 +296,10 @@  int arch_set_info_hvm_guest(struct vcpu *v, const vcpu_hvm_context_t *ctx)
     if ( hvm_paging_enabled(v) && !paging_mode_hap(v->domain) )
     {
         /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
-        struct page_info *page = get_page_from_gfn(v->domain,
-                                 v->arch.hvm.guest_cr[3] >> PAGE_SHIFT,
+        struct page_info *page;
+
+        page = get_page_from_gfn(v->domain,
+                                 gaddr_to_gfn(v->arch.hvm.guest_cr[3]),
                                  NULL, P2M_ALLOC);
         if ( !page )
         {
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 029eea3b85..236bd6ed38 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2168,7 +2168,7 @@  int hvm_set_cr0(unsigned long value, bool may_defer)
 {
     struct vcpu *v = current;
     struct domain *d = v->domain;
-    unsigned long gfn, old_value = v->arch.hvm.guest_cr[0];
+    unsigned long old_value = v->arch.hvm.guest_cr[0];
     struct page_info *page;
 
     HVM_DBG_LOG(DBG_LEVEL_VMMU, "Update CR0 value = %lx", value);
@@ -2223,7 +2223,8 @@  int hvm_set_cr0(unsigned long value, bool may_defer)
         if ( !paging_mode_hap(d) )
         {
             /* The guest CR3 must be pointing to the guest physical. */
-            gfn = v->arch.hvm.guest_cr[3] >> PAGE_SHIFT;
+            gfn_t gfn = gaddr_to_gfn(v->arch.hvm.guest_cr[3]);
+
             page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
             if ( !page )
             {
@@ -2315,7 +2316,7 @@  int hvm_set_cr3(unsigned long value, bool may_defer)
     {
         /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
         HVM_DBG_LOG(DBG_LEVEL_VMMU, "CR3 value = %lx", value);
-        page = get_page_from_gfn(v->domain, value >> PAGE_SHIFT,
+        page = get_page_from_gfn(v->domain, gaddr_to_gfn(value),
                                  NULL, P2M_ALLOC);
         if ( !page )
             goto bad_cr3;
@@ -3143,7 +3144,7 @@  enum hvm_translation_result hvm_translate_get_page(
          && hvm_mmio_internal(gfn_to_gaddr(gfn)) )
         return HVMTRANS_bad_gfn_to_mfn;
 
-    page = get_page_from_gfn(v->domain, gfn_x(gfn), &p2mt, P2M_UNSHARE);
+    page = get_page_from_gfn(v->domain, gfn, &p2mt, P2M_UNSHARE);
 
     if ( !page )
         return HVMTRANS_bad_gfn_to_mfn;
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index cf83ce9a19..620eb951b6 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -317,7 +317,7 @@  static int svm_vmcb_restore(struct vcpu *v, struct hvm_hw_cpu *c)
     {
         if ( c->cr0 & X86_CR0_PG )
         {
-            page = get_page_from_gfn(v->domain, c->cr3 >> PAGE_SHIFT,
+            page = get_page_from_gfn(v->domain, gaddr_to_gfn(c->cr3),
                                      NULL, P2M_ALLOC);
             if ( !page )
             {
@@ -2276,9 +2276,9 @@  nsvm_get_nvmcb_page(struct vcpu *v, uint64_t vmcbaddr)
         return NULL;
 
     /* Need to translate L1-GPA to MPA */
-    page = get_page_from_gfn(v->domain, 
-                            nv->nv_vvmcxaddr >> PAGE_SHIFT, 
-                            &p2mt, P2M_ALLOC | P2M_UNSHARE);
+    page = get_page_from_gfn(v->domain,
+                             gaddr_to_gfn(nv->nv_vvmcxaddr),
+                             &p2mt, P2M_ALLOC | P2M_UNSHARE);
     if ( !page )
         return NULL;
 
diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c
index 4b06b78a27..b393a1457b 100644
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -256,16 +256,16 @@  static void dump_hypercall(const struct domain *d)
 
 static void enable_hypercall_page(struct domain *d)
 {
-    unsigned long gmfn = d->arch.hvm.viridian->hypercall_gpa.pfn;
-    struct page_info *page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
+    gfn_t gfn = _gfn(d->arch.hvm.viridian->hypercall_gpa.pfn);
+    struct page_info *page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
     uint8_t *p;
 
     if ( !page || !get_page_type(page, PGT_writable_page) )
     {
         if ( page )
             put_page(page);
-        gdprintk(XENLOG_WARNING, "Bad GMFN %#"PRI_gfn" (MFN %#"PRI_mfn")\n",
-                 gmfn, mfn_x(page ? page_to_mfn(page) : INVALID_MFN));
+        gdprintk(XENLOG_WARNING, "Bad GFN %#"PRI_gfn" (MFN %#"PRI_mfn")\n",
+                 gfn_x(gfn), mfn_x(page ? page_to_mfn(page) : INVALID_MFN));
         return;
     }
 
@@ -733,13 +733,13 @@  void viridian_dump_guest_page(const struct vcpu *v, const char *name,
 
 void viridian_map_guest_page(struct domain *d, struct viridian_page *vp)
 {
-    unsigned long gmfn = vp->msr.pfn;
+    gfn_t gfn = _gfn(vp->msr.pfn);
     struct page_info *page;
 
     if ( vp->ptr )
         return;
 
-    page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
+    page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
     if ( !page )
         goto fail;
 
@@ -760,8 +760,8 @@  void viridian_map_guest_page(struct domain *d, struct viridian_page *vp)
     return;
 
  fail:
-    gdprintk(XENLOG_WARNING, "Bad GMFN %#"PRI_gfn" (MFN %#"PRI_mfn")\n",
-             gmfn, mfn_x(page ? page_to_mfn(page) : INVALID_MFN));
+    gdprintk(XENLOG_WARNING, "Bad GFN %#"PRI_gfn" (MFN %#"PRI_mfn")\n",
+             gfn_x(gfn), mfn_x(page ? page_to_mfn(page) : INVALID_MFN));
 }
 
 void viridian_unmap_guest_page(struct viridian_page *vp)
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 0060310d74..38bdef0862 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -674,7 +674,7 @@  static int vmx_restore_cr0_cr3(
     {
         if ( cr0 & X86_CR0_PG )
         {
-            page = get_page_from_gfn(v->domain, cr3 >> PAGE_SHIFT,
+            page = get_page_from_gfn(v->domain, gaddr_to_gfn(cr3),
                                      NULL, P2M_ALLOC);
             if ( !page )
             {
@@ -1314,7 +1314,7 @@  static void vmx_load_pdptrs(struct vcpu *v)
     if ( (cr3 & 0x1fUL) && !hvm_pcid_enabled(v) )
         goto crash;
 
-    page = get_page_from_gfn(v->domain, cr3 >> PAGE_SHIFT, &p2mt, P2M_UNSHARE);
+    page = get_page_from_gfn(v->domain, gaddr_to_gfn(cr3), &p2mt, P2M_UNSHARE);
     if ( !page )
     {
         /* Ideally you don't want to crash but rather go into a wait 
diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index fdf449bfd1..c93ae59921 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -646,11 +646,11 @@  static void nvmx_update_apic_access_address(struct vcpu *v)
     if ( ctrl & SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES )
     {
         p2m_type_t p2mt;
-        unsigned long apic_gpfn;
+        gfn_t apic_gfn;
         struct page_info *apic_pg;
 
-        apic_gpfn = get_vvmcs(v, APIC_ACCESS_ADDR) >> PAGE_SHIFT;
-        apic_pg = get_page_from_gfn(v->domain, apic_gpfn, &p2mt, P2M_ALLOC);
+        apic_gfn = gaddr_to_gfn(get_vvmcs(v, APIC_ACCESS_ADDR));
+        apic_pg = get_page_from_gfn(v->domain, apic_gfn, &p2mt, P2M_ALLOC);
         ASSERT(apic_pg && !p2m_is_paging(p2mt));
         __vmwrite(APIC_ACCESS_ADDR, page_to_maddr(apic_pg));
         put_page(apic_pg);
@@ -667,11 +667,11 @@  static void nvmx_update_virtual_apic_address(struct vcpu *v)
     if ( ctrl & CPU_BASED_TPR_SHADOW )
     {
         p2m_type_t p2mt;
-        unsigned long vapic_gpfn;
+        gfn_t vapic_gfn;
         struct page_info *vapic_pg;
 
-        vapic_gpfn = get_vvmcs(v, VIRTUAL_APIC_PAGE_ADDR) >> PAGE_SHIFT;
-        vapic_pg = get_page_from_gfn(v->domain, vapic_gpfn, &p2mt, P2M_ALLOC);
+        vapic_gfn = gaddr_to_gfn(get_vvmcs(v, VIRTUAL_APIC_PAGE_ADDR));
+        vapic_pg = get_page_from_gfn(v->domain, vapic_gfn, &p2mt, P2M_ALLOC);
         ASSERT(vapic_pg && !p2m_is_paging(p2mt));
         __vmwrite(VIRTUAL_APIC_PAGE_ADDR, page_to_maddr(vapic_pg));
         put_page(vapic_pg);
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 7531406543..f8e2b6f921 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2083,7 +2083,7 @@  static int mod_l1_entry(l1_pgentry_t *pl1e, l1_pgentry_t nl1e,
             p2m_query_t q = l1e_get_flags(nl1e) & _PAGE_RW ?
                             P2M_ALLOC | P2M_UNSHARE : P2M_ALLOC;
 
-            page = get_page_from_gfn(pg_dom, l1e_get_pfn(nl1e), &p2mt, q);
+            page = get_page_from_gfn(pg_dom, _gfn(l1e_get_pfn(nl1e)), &p2mt, q);
 
             if ( p2m_is_paged(p2mt) )
             {
@@ -3307,7 +3307,8 @@  long do_mmuext_op(
             if ( paging_mode_refcounts(pg_owner) )
                 break;
 
-            page = get_page_from_gfn(pg_owner, op.arg1.mfn, NULL, P2M_ALLOC);
+            page = get_page_from_gfn(pg_owner, _gfn(op.arg1.mfn), NULL,
+                                     P2M_ALLOC);
             if ( unlikely(!page) )
             {
                 rc = -EINVAL;
@@ -3372,7 +3373,8 @@  long do_mmuext_op(
             if ( paging_mode_refcounts(pg_owner) )
                 break;
 
-            page = get_page_from_gfn(pg_owner, op.arg1.mfn, NULL, P2M_ALLOC);
+            page = get_page_from_gfn(pg_owner, _gfn(op.arg1.mfn), NULL,
+                                     P2M_ALLOC);
             if ( unlikely(!page) )
             {
                 gdprintk(XENLOG_WARNING,
@@ -3588,7 +3590,8 @@  long do_mmuext_op(
         }
 
         case MMUEXT_CLEAR_PAGE:
-            page = get_page_from_gfn(pg_owner, op.arg1.mfn, &p2mt, P2M_ALLOC);
+            page = get_page_from_gfn(pg_owner, _gfn(op.arg1.mfn), &p2mt,
+                                     P2M_ALLOC);
             if ( unlikely(p2mt != p2m_ram_rw) && page )
             {
                 put_page(page);
@@ -3616,7 +3619,7 @@  long do_mmuext_op(
         {
             struct page_info *src_page, *dst_page;
 
-            src_page = get_page_from_gfn(pg_owner, op.arg2.src_mfn, &p2mt,
+            src_page = get_page_from_gfn(pg_owner, _gfn(op.arg2.src_mfn), &p2mt,
                                          P2M_ALLOC);
             if ( unlikely(p2mt != p2m_ram_rw) && src_page )
             {
@@ -3632,7 +3635,7 @@  long do_mmuext_op(
                 break;
             }
 
-            dst_page = get_page_from_gfn(pg_owner, op.arg1.mfn, &p2mt,
+            dst_page = get_page_from_gfn(pg_owner, _gfn(op.arg1.mfn), &p2mt,
                                          P2M_ALLOC);
             if ( unlikely(p2mt != p2m_ram_rw) && dst_page )
             {
@@ -3720,7 +3723,8 @@  long do_mmu_update(
 {
     struct mmu_update req;
     void *va = NULL;
-    unsigned long gpfn, gmfn;
+    unsigned long gpfn;
+    gfn_t gfn;
     struct page_info *page;
     unsigned int cmd, i = 0, done = 0, pt_dom;
     struct vcpu *curr = current, *v = curr;
@@ -3833,8 +3837,8 @@  long do_mmu_update(
             rc = -EINVAL;
 
             req.ptr -= cmd;
-            gmfn = req.ptr >> PAGE_SHIFT;
-            page = get_page_from_gfn(pt_owner, gmfn, &p2mt, P2M_ALLOC);
+            gfn = gaddr_to_gfn(req.ptr);
+            page = get_page_from_gfn(pt_owner, gfn, &p2mt, P2M_ALLOC);
 
             if ( unlikely(!page) || p2mt != p2m_ram_rw )
             {
@@ -3842,7 +3846,7 @@  long do_mmu_update(
                     put_page(page);
                 if ( p2m_is_paged(p2mt) )
                 {
-                    p2m_mem_paging_populate(pt_owner, gmfn);
+                    p2m_mem_paging_populate(pt_owner, gfn_x(gfn));
                     rc = -ENOENT;
                 }
                 else
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 4b1e38b131..4ca35b56d6 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -2956,7 +2956,7 @@  int p2m_add_foreign(struct domain *tdom, unsigned long fgfn,
      * Take a refcnt on the mfn. NB: following supported for foreign mapping:
      *     ram_rw | ram_logdirty | ram_ro | paging_out.
      */
-    page = get_page_from_gfn(fdom, fgfn, &p2mt, P2M_ALLOC);
+    page = get_page_from_gfn(fdom, _gfn(fgfn), &p2mt, P2M_ALLOC);
     if ( !page ||
          !p2m_is_ram(p2mt) || p2m_is_shared(p2mt) || p2m_is_hole(p2mt) )
     {
diff --git a/xen/arch/x86/mm/shadow/hvm.c b/xen/arch/x86/mm/shadow/hvm.c
index 0aa560b7f5..1315597878 100644
--- a/xen/arch/x86/mm/shadow/hvm.c
+++ b/xen/arch/x86/mm/shadow/hvm.c
@@ -388,15 +388,15 @@  void shadow_continue_emulation(struct sh_emulate_ctxt *sh_ctxt,
 static mfn_t emulate_gva_to_mfn(struct vcpu *v, unsigned long vaddr,
                                 struct sh_emulate_ctxt *sh_ctxt)
 {
-    unsigned long gfn;
+    gfn_t gfn;
     struct page_info *page;
     mfn_t mfn;
     p2m_type_t p2mt;
     uint32_t pfec = PFEC_page_present | PFEC_write_access;
 
     /* Translate the VA to a GFN. */
-    gfn = paging_get_hostmode(v)->gva_to_gfn(v, NULL, vaddr, &pfec);
-    if ( gfn == gfn_x(INVALID_GFN) )
+    gfn = _gfn(paging_get_hostmode(v)->gva_to_gfn(v, NULL, vaddr, &pfec));
+    if ( gfn_eq(gfn, INVALID_GFN) )
     {
         x86_emul_pagefault(pfec, vaddr, &sh_ctxt->ctxt);
 
diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
index 3a3c15890b..4f3f438614 100644
--- a/xen/arch/x86/physdev.c
+++ b/xen/arch/x86/physdev.c
@@ -229,7 +229,8 @@  ret_t do_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
             break;
 
         ret = -EINVAL;
-        page = get_page_from_gfn(current->domain, info.gmfn, NULL, P2M_ALLOC);
+        page = get_page_from_gfn(current->domain, _gfn(info.gmfn),
+                                 NULL, P2M_ALLOC);
         if ( !page )
             break;
         if ( !get_page_type(page, PGT_writable_page) )
diff --git a/xen/arch/x86/pv/descriptor-tables.c b/xen/arch/x86/pv/descriptor-tables.c
index 940804b18a..7b3fb2806a 100644
--- a/xen/arch/x86/pv/descriptor-tables.c
+++ b/xen/arch/x86/pv/descriptor-tables.c
@@ -112,7 +112,7 @@  long pv_set_gdt(struct vcpu *v, unsigned long *frames, unsigned int entries)
     {
         struct page_info *page;
 
-        page = get_page_from_gfn(d, frames[i], NULL, P2M_ALLOC);
+        page = get_page_from_gfn(d, _gfn(frames[i]), NULL, P2M_ALLOC);
         if ( !page )
             goto fail;
         if ( !get_page_type(page, PGT_seg_desc_page) )
@@ -219,7 +219,7 @@  long do_update_descriptor(uint64_t gaddr, seg_desc_t d)
     if ( !IS_ALIGNED(gaddr, sizeof(d)) || !check_descriptor(currd, &d) )
         return -EINVAL;
 
-    page = get_page_from_gfn(currd, gfn_x(gfn), NULL, P2M_ALLOC);
+    page = get_page_from_gfn(currd, gfn, NULL, P2M_ALLOC);
     if ( !page )
         return -EINVAL;
 
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 8a4909bf4c..77ffa7fdcf 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -756,12 +756,12 @@  static int write_cr(unsigned int reg, unsigned long val,
     case 3: /* Write CR3 */
     {
         struct domain *currd = curr->domain;
-        unsigned long gfn;
+        gfn_t gfn;
         struct page_info *page;
         int rc;
 
-        gfn = !is_pv_32bit_domain(currd)
-              ? xen_cr3_to_pfn(val) : compat_cr3_to_pfn(val);
+        gfn = _gfn(!is_pv_32bit_domain(currd)
+                   ? xen_cr3_to_pfn(val) : compat_cr3_to_pfn(val));
         page = get_page_from_gfn(currd, gfn, NULL, P2M_ALLOC);
         if ( !page )
             break;
diff --git a/xen/arch/x86/pv/mm.c b/xen/arch/x86/pv/mm.c
index f5ea00ca4e..c9ad1152b4 100644
--- a/xen/arch/x86/pv/mm.c
+++ b/xen/arch/x86/pv/mm.c
@@ -106,7 +106,7 @@  bool pv_map_ldt_shadow_page(unsigned int offset)
     if ( unlikely(!(l1e_get_flags(gl1e) & _PAGE_PRESENT)) )
         return false;
 
-    page = get_page_from_gfn(currd, l1e_get_pfn(gl1e), NULL, P2M_ALLOC);
+    page = get_page_from_gfn(currd, _gfn(l1e_get_pfn(gl1e)), NULL, P2M_ALLOC);
     if ( unlikely(!page) )
         return false;
 
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 23069e25ec..d8f8070ac9 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -803,7 +803,7 @@  int guest_wrmsr_xen(struct vcpu *v, uint32_t idx, uint64_t val)
     case 0: /* Write hypercall page */
     {
         void *hypercall_page;
-        unsigned long gmfn = val >> PAGE_SHIFT;
+        gfn_t gfn = gaddr_to_gfn(val);
         unsigned int page_index = val & (PAGE_SIZE - 1);
         struct page_info *page;
         p2m_type_t t;
@@ -816,7 +816,7 @@  int guest_wrmsr_xen(struct vcpu *v, uint32_t idx, uint64_t val)
             return X86EMUL_EXCEPTION;
         }
 
-        page = get_page_from_gfn(d, gmfn, &t, P2M_ALLOC);
+        page = get_page_from_gfn(d, gfn, &t, P2M_ALLOC);
 
         if ( !page || !get_page_type(page, PGT_writable_page) )
         {
@@ -825,13 +825,14 @@  int guest_wrmsr_xen(struct vcpu *v, uint32_t idx, uint64_t val)
 
             if ( p2m_is_paging(t) )
             {
-                p2m_mem_paging_populate(d, gmfn);
+                p2m_mem_paging_populate(d, gfn_x(gfn));
                 return X86EMUL_RETRY;
             }
 
             gdprintk(XENLOG_WARNING,
-                     "Bad GMFN %lx (MFN %#"PRI_mfn") to MSR %08x\n",
-                     gmfn, mfn_x(page ? page_to_mfn(page) : INVALID_MFN), base);
+                     "Bad GFN %#"PRI_gfn" (MFN %#"PRI_mfn") to MSR %08x\n",
+                     gfn_x(gfn), mfn_x(page ? page_to_mfn(page) : INVALID_MFN),
+                     base);
             return X86EMUL_EXCEPTION;
         }
 
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 744b572195..e8f6dfbdf1 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1299,7 +1299,7 @@  int map_vcpu_info(struct vcpu *v, unsigned long gfn, unsigned offset)
     if ( (v != current) && !(v->pause_flags & VPF_down) )
         return -EINVAL;
 
-    page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
+    page = get_page_from_gfn(d, _gfn(gfn), NULL, P2M_ALLOC);
     if ( !page )
         return -EINVAL;
 
diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 230f440f14..073981ab43 100644
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -361,7 +361,7 @@  static const struct evtchn_port_ops evtchn_port_ops_fifo =
     .print_state   = evtchn_fifo_print_state,
 };
 
-static int map_guest_page(struct domain *d, uint64_t gfn, void **virt)
+static int map_guest_page(struct domain *d, gfn_t gfn, void **virt)
 {
     struct page_info *p;
 
@@ -422,7 +422,7 @@  static int setup_control_block(struct vcpu *v)
     return 0;
 }
 
-static int map_control_block(struct vcpu *v, uint64_t gfn, uint32_t offset)
+static int map_control_block(struct vcpu *v, gfn_t gfn, uint32_t offset)
 {
     void *virt;
     unsigned int i;
@@ -508,7 +508,7 @@  int evtchn_fifo_init_control(struct evtchn_init_control *init_control)
 {
     struct domain *d = current->domain;
     uint32_t vcpu_id;
-    uint64_t gfn;
+    gfn_t gfn;
     uint32_t offset;
     struct vcpu *v;
     int rc;
@@ -516,7 +516,7 @@  int evtchn_fifo_init_control(struct evtchn_init_control *init_control)
     init_control->link_bits = EVTCHN_FIFO_LINK_BITS;
 
     vcpu_id = init_control->vcpu;
-    gfn     = init_control->control_gfn;
+    gfn     = _gfn(init_control->control_gfn);
     offset  = init_control->offset;
 
     if ( (v = domain_vcpu(d, vcpu_id)) == NULL )
@@ -578,7 +578,7 @@  int evtchn_fifo_init_control(struct evtchn_init_control *init_control)
     return rc;
 }
 
-static int add_page_to_event_array(struct domain *d, unsigned long gfn)
+static int add_page_to_event_array(struct domain *d, gfn_t gfn)
 {
     void *virt;
     unsigned int slot;
@@ -628,7 +628,7 @@  int evtchn_fifo_expand_array(const struct evtchn_expand_array *expand_array)
         return -EOPNOTSUPP;
 
     spin_lock(&d->event_lock);
-    rc = add_page_to_event_array(d, expand_array->array_gfn);
+    rc = add_page_to_event_array(d, _gfn(expand_array->array_gfn));
     spin_unlock(&d->event_lock);
 
     return rc;
diff --git a/xen/common/memory.c b/xen/common/memory.c
index d9b35a608c..2634a8b762 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1393,7 +1393,7 @@  long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
             return rc;
         }
 
-        page = get_page_from_gfn(d, xrfp.gpfn, NULL, P2M_ALLOC);
+        page = get_page_from_gfn(d, _gfn(xrfp.gpfn), NULL, P2M_ALLOC);
         if ( page )
         {
             rc = guest_physmap_remove_page(d, _gfn(xrfp.gpfn),
@@ -1664,7 +1664,7 @@  int check_get_page_from_gfn(struct domain *d, gfn_t gfn, bool readonly,
     p2m_type_t p2mt;
     struct page_info *page;
 
-    page = get_page_from_gfn(d, gfn_x(gfn), &p2mt, q);
+    page = get_page_from_gfn(d, gfn, &p2mt, q);
 
 #ifdef CONFIG_HAS_MEM_PAGING
     if ( p2m_is_paging(p2mt) )
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 03f2ee75c1..5e50596fcb 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -298,7 +298,7 @@  struct page_info *p2m_get_page_from_gfn(struct domain *d, gfn_t gfn,
                                         p2m_type_t *t);
 
 static inline struct page_info *get_page_from_gfn(
-    struct domain *d, unsigned long gfn, p2m_type_t *t, p2m_query_t q)
+    struct domain *d, gfn_t gfn, p2m_type_t *t, p2m_query_t q)
 {
     mfn_t mfn;
     p2m_type_t _t;
@@ -309,7 +309,7 @@  static inline struct page_info *get_page_from_gfn(
      * not auto-translated.
      */
     if ( likely(d != dom_xen) )
-        return p2m_get_page_from_gfn(d, _gfn(gfn), t);
+        return p2m_get_page_from_gfn(d, gfn, t);
 
     if ( !t )
         t = &_t;
@@ -320,7 +320,7 @@  static inline struct page_info *get_page_from_gfn(
      * DOMID_XEN sees 1-1 RAM. The p2m_type is based on the type of the
      * page.
      */
-    mfn = _mfn(gfn);
+    mfn = _mfn(gfn_x(gfn));
     page = mfn_to_page(mfn);
 
     if ( !mfn_valid(mfn) || !get_page(page, d) )
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 94285db1b4..ff4528baf9 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -491,18 +491,26 @@  struct page_info *p2m_get_page_from_gfn(struct p2m_domain *p2m, gfn_t gfn,
                                         p2m_query_t q);
 
 static inline struct page_info *get_page_from_gfn(
-    struct domain *d, unsigned long gfn, p2m_type_t *t, p2m_query_t q)
+    struct domain *d, gfn_t gfn, p2m_type_t *t, p2m_query_t q)
 {
     struct page_info *page;
+    mfn_t mfn;
 
     if ( paging_mode_translate(d) )
-        return p2m_get_page_from_gfn(p2m_get_hostp2m(d), _gfn(gfn), t, NULL, q);
+        return p2m_get_page_from_gfn(p2m_get_hostp2m(d), gfn, t, NULL, q);
 
     /* Non-translated guests see 1-1 RAM / MMIO mappings everywhere */
     if ( t )
         *t = likely(d != dom_io) ? p2m_ram_rw : p2m_mmio_direct;
-    page = mfn_to_page(_mfn(gfn));
-    return mfn_valid(_mfn(gfn)) && get_page(page, d) ? page : NULL;
+
+    mfn = _mfn(gfn_x(gfn));
+
+    if ( !mfn_valid(mfn) )
+        return NULL;
+
+    page = mfn_to_page(mfn);
+
+    return get_page(page, d) ? page : NULL;
 }
 
 /* General conversion function from mfn to gfn */