[Xen-devel,15/20] xen/arm: mm: Use the shorter version __aligned(PAGE_SIZE) to align page-tables

Message ID 20190422164937.21350-16-julien.grall@arm.com
State New
Headers show
Series
  • xen/arm: Clean-up & fixes in boot/mm code
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Commit Message

Julien Grall April 22, 2019, 4:49 p.m.
We currently use the very long version __attribute__((__aligned(4096)))
to align page-tables. Thankfully there is a shorter version to make
the code more readable.

While modifying the attribute:
    1) Move it before the variable name as we do in other part of Xen
    2) Switch to PAGE_SIZE instead of 4096 to make more future-proof
    3) Mark static page-tables not used outside the file (i.e any
       page-tables other than boot_* and xen_fixmap).

Lastly, some of the variables use __attribute__(__aligned(X * 4096)).
However this is not necessary as page-tables are only required to be
to be aligned to a page-size. So use __aligned(PAGE_SIZE).

Signed-off-by: Julien Grall <julien.grall@arm.com>
---
 xen/arch/arm/mm.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

Comments

Andrii Anisov May 3, 2019, 3:58 p.m. | #1
On 22.04.19 19:49, Julien Grall wrote:
> We currently use the very long version __attribute__((__aligned(4096)))
> to align page-tables. Thankfully there is a shorter version to make

IMO it is better to change `version` to `macro`. In order to specify it is not a compiler specific but specific to XEN.

> the code more readable.
> 
> While modifying the attribute:
>      1) Move it before the variable name as we do in other part of Xen
>      2) Switch to PAGE_SIZE instead of 4096 to make more future-proof
>      3) Mark static page-tables not used outside the file (i.e any
>         page-tables other than boot_* and xen_fixmap).
> 
> Lastly, some of the variables use __attribute__(__aligned(X * 4096)).
> However this is not necessary as page-tables are only required to be
> to be aligned to a page-size. So use __aligned(PAGE_SIZE).
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>
Though:

Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
Julien Grall May 3, 2019, 5:09 p.m. | #2
On 03/05/2019 16:58, Andrii Anisov wrote:
> 
> 
> On 22.04.19 19:49, Julien Grall wrote:
>> We currently use the very long version __attribute__((__aligned(4096)))
>> to align page-tables. Thankfully there is a shorter version to make
> 
> IMO it is better to change `version` to `macro`. In order to specify it is not a 
> compiler specific but specific to XEN.

I will reword to "Thankfully Xen provides an handy macro that will make the code 
more readable".

> 
>> the code more readable.
>>
>> While modifying the attribute:
>>      1) Move it before the variable name as we do in other part of Xen
>>      2) Switch to PAGE_SIZE instead of 4096 to make more future-proof
>>      3) Mark static page-tables not used outside the file (i.e any
>>         page-tables other than boot_* and xen_fixmap).
>>
>> Lastly, some of the variables use __attribute__(__aligned(X * 4096)).
>> However this is not necessary as page-tables are only required to be
>> to be aligned to a page-size. So use __aligned(PAGE_SIZE).
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
> Though:
> 
> Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
> 

Cheers,
Andrii Anisov May 6, 2019, 7:19 a.m. | #3
On 03.05.19 20:09, Julien Grall wrote:
> I will reword to "Thankfully Xen provides an handy macro that will make the code more readable".

Good.

Patch

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 6db7dda0da..fa0f41bd07 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -73,13 +73,13 @@  struct domain *dom_xen, *dom_io, *dom_cow;
  * Finally, if EARLY_PRINTK is enabled then xen_fixmap will be mapped
  * by the CPU once it has moved off the 1:1 mapping.
  */
-lpae_t boot_pgtable[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+lpae_t __aligned(PAGE_SIZE) boot_pgtable[LPAE_ENTRIES];
 #ifdef CONFIG_ARM_64
-lpae_t boot_first[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
-lpae_t boot_first_id[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+lpae_t __aligned(PAGE_SIZE) boot_first[LPAE_ENTRIES];
+lpae_t __aligned(PAGE_SIZE) boot_first_id[LPAE_ENTRIES];
 #endif
-lpae_t boot_second[LPAE_ENTRIES]  __attribute__((__aligned__(4096)));
-lpae_t boot_third[LPAE_ENTRIES]  __attribute__((__aligned__(4096)));
+lpae_t __aligned(PAGE_SIZE) boot_second[LPAE_ENTRIES];
+lpae_t __aligned(PAGE_SIZE) boot_third[LPAE_ENTRIES];
 
 /* Main runtime page tables */
 
@@ -93,8 +93,8 @@  lpae_t boot_third[LPAE_ENTRIES]  __attribute__((__aligned__(4096)));
 
 #ifdef CONFIG_ARM_64
 #define HYP_PT_ROOT_LEVEL 0
-lpae_t xen_pgtable[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
-lpae_t xen_first[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+static lpae_t __aligned(PAGE_SIZE) xen_pgtable[LPAE_ENTRIES];
+static lpae_t __aligned(PAGE_SIZE) xen_first[LPAE_ENTRIES];
 #define THIS_CPU_PGTABLE xen_pgtable
 #else
 #define HYP_PT_ROOT_LEVEL 1
@@ -107,17 +107,16 @@  static DEFINE_PER_CPU(lpae_t *, xen_pgtable);
  * DOMHEAP_VIRT_START...DOMHEAP_VIRT_END in 2MB chunks. */
 static DEFINE_PER_CPU(lpae_t *, xen_dommap);
 /* Root of the trie for cpu0, other CPU's PTs are dynamically allocated */
-lpae_t cpu0_pgtable[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+static lpae_t __aligned(PAGE_SIZE) cpu0_pgtable[LPAE_ENTRIES];
 /* cpu0's domheap page tables */
-lpae_t cpu0_dommap[LPAE_ENTRIES*DOMHEAP_SECOND_PAGES]
-    __attribute__((__aligned__(4096*DOMHEAP_SECOND_PAGES)));
+static lpae_t __aligned(PAGE_SIZE) cpu0_dommap[LPAE_ENTRIES*DOMHEAP_SECOND_PAGES];
 #endif
 
 #ifdef CONFIG_ARM_64
 /* The first page of the first level mapping of the xenheap. The
  * subsequent xenheap first level pages are dynamically allocated, but
  * we need this one to bootstrap ourselves. */
-lpae_t xenheap_first_first[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+static lpae_t __aligned(PAGE_SIZE) xenheap_first_first[LPAE_ENTRIES];
 /* The zeroeth level slot which uses xenheap_first_first. Used because
  * setup_xenheap_mappings otherwise relies on mfn_to_virt which isn't
  * valid for a non-xenheap mapping. */
@@ -131,12 +130,12 @@  static __initdata int xenheap_first_first_slot = -1;
  * addresses from 0 to 0x7fffffff. Offsets into it are calculated
  * with second_linear_offset(), not second_table_offset().
  */
-lpae_t xen_second[LPAE_ENTRIES*2] __attribute__((__aligned__(4096*2)));
+static lpae_t __aligned(PAGE_SIZE) xen_second[LPAE_ENTRIES*2];
 /* First level page table used for fixmap */
-lpae_t xen_fixmap[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+lpae_t __aligned(PAGE_SIZE) xen_fixmap[LPAE_ENTRIES];
 /* First level page table used to map Xen itself with the XN bit set
  * as appropriate. */
-static lpae_t xen_xenmap[LPAE_ENTRIES] __attribute__((__aligned__(4096)));
+static lpae_t __aligned(PAGE_SIZE) xen_xenmap[LPAE_ENTRIES];
 
 /* Non-boot CPUs use this to find the correct pagetables. */
 uint64_t init_ttbr;