| Message ID | 1424964547-2118-2-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 26 February 2015 at 16:10, Marc Zyngier <marc.zyngier@arm.com> wrote: > On 26/02/15 15:29, Ard Biesheuvel wrote: >> The HYP init bounce page is a runtime construct that ensures that the >> HYP init code does not cross a page boundary. However, this is something >> we can do perfectly well at build time, by aligning the code appropriately. >> >> For arm64, we just align to 4 KB, and enforce that the code size is less >> than 4 KB, regardless of the chosen page size. >> >> For ARM, the whole code is less than 256 bytes, so we tweak the linker >> script to align at a power of 2 upper bound of the code size >> >> Note that this also fixes a benign off-by-one error in the original bounce >> page code, where a bounce page would be allocated unnecessarily if the code >> was exactly 1 page in size. > > I really like this simplification. Can you please check that it still > work on 32bit with this patch from Arnd? > > https://www.mail-archive.com/kvm@vger.kernel.org/msg112364.html > Yes, it does. Note that the kernel's RODATA permissions shouldn't affect whether this code is executable or not in HYP mode, so I think this code belongs in RODATA in the 1st place. > Another question below: > >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> >> --- >> arch/arm/kernel/vmlinux.lds.S | 12 +++++++++--- >> arch/arm/kvm/init.S | 11 +++++++++++ >> arch/arm/kvm/mmu.c | 42 +++++------------------------------------ >> arch/arm64/kernel/vmlinux.lds.S | 18 ++++++++++++------ >> 4 files changed, 37 insertions(+), 46 deletions(-) >> >> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S >> index b31aa73e8076..8179d3903dee 100644 >> --- a/arch/arm/kernel/vmlinux.lds.S >> +++ b/arch/arm/kernel/vmlinux.lds.S >> @@ -23,7 +23,7 @@ >> VMLINUX_SYMBOL(__idmap_text_start) = .; \ >> *(.idmap.text) \ >> VMLINUX_SYMBOL(__idmap_text_end) = .; \ >> - . = ALIGN(32); \ >> + . = ALIGN(1 << __hyp_idmap_align_order); \ >> VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \ >> *(.hyp.idmap.text) \ >> VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; >> @@ -346,8 +346,14 @@ SECTIONS >> */ >> ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support") >> ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined") >> + >> /* >> - * The HYP init code can't be more than a page long. >> + * The HYP init code can't be more than a page long, >> + * and should not cross a page boundary. >> * The above comment applies as well. >> */ >> -ASSERT(((__hyp_idmap_text_end - __hyp_idmap_text_start) <= PAGE_SIZE), "HYP init code too big") >> +ASSERT(((__hyp_idmap_text_end - 1) & PAGE_MASK) - >> + (__hyp_idmap_text_start & PAGE_MASK) == 0, >> + "HYP init code too big or unaligned") >> +ASSERT(__hyp_idmap_size <= (1 << __hyp_idmap_align_order), >> + "__hyp_idmap_size should be <= (1 << __hyp_idmap_align_order)") >> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S >> index 3988e72d16ff..7a279bc8e0e1 100644 >> --- a/arch/arm/kvm/init.S >> +++ b/arch/arm/kvm/init.S >> @@ -157,3 +157,14 @@ target: @ We're now in the trampoline code, switch page tables >> __kvm_hyp_init_end: >> >> .popsection >> + >> + /* >> + * When making changes to this file, make sure that the value of >> + * __hyp_idmap_align_order is updated if the size of the code ends up >> + * exceeding (1 << __hyp_idmap_align_order). This helps ensure that the >> + * code never crosses a page boundary, without wasting too much memory >> + * on aligning to PAGE_SIZE. >> + */ >> + .global __hyp_idmap_size, __hyp_idmap_align_order >> + .set __hyp_idmap_size, __kvm_hyp_init_end - __kvm_hyp_init >> + .set __hyp_idmap_align_order, 8 > > Is there a way to generate this __hyp_idmap_align_order automatically? > We're already pretty close to this 8 bit limit... > This seems to work: #define HYP_IDMAP_ALIGN \ __hyp_idmap_size <= 0x100 ? 0x100 : \ __hyp_idmap_size <= 0x200 ? 0x200 : \ __hyp_idmap_size <= 0x400 ? 0x400 : \ __hyp_idmap_size <= 0x800 ? 0x800 : 0x1000 and . = ALIGN(HYP_IDMAP_ALIGN); \ and we are limited at 1 page anyway. Should I respin and include the move to RODATA at the same time? Or would you like me to rebase onto Arnd's patch?
On 26 February 2015 at 18:24, Marc Zyngier <marc.zyngier@arm.com> wrote: > On 26/02/15 17:31, Ard Biesheuvel wrote: >> On 26 February 2015 at 16:10, Marc Zyngier <marc.zyngier@arm.com> wrote: >>> On 26/02/15 15:29, Ard Biesheuvel wrote: >>>> The HYP init bounce page is a runtime construct that ensures that the >>>> HYP init code does not cross a page boundary. However, this is something >>>> we can do perfectly well at build time, by aligning the code appropriately. >>>> >>>> For arm64, we just align to 4 KB, and enforce that the code size is less >>>> than 4 KB, regardless of the chosen page size. >>>> >>>> For ARM, the whole code is less than 256 bytes, so we tweak the linker >>>> script to align at a power of 2 upper bound of the code size >>>> >>>> Note that this also fixes a benign off-by-one error in the original bounce >>>> page code, where a bounce page would be allocated unnecessarily if the code >>>> was exactly 1 page in size. >>> >>> I really like this simplification. Can you please check that it still >>> work on 32bit with this patch from Arnd? >>> >>> https://www.mail-archive.com/kvm@vger.kernel.org/msg112364.html >>> >> >> Yes, it does. >> >> Note that the kernel's RODATA permissions shouldn't affect whether >> this code is executable or not in HYP mode, so I think this code >> belongs in RODATA in the 1st place. > > Yup. Maybe we should do the same for arm64, shouldn't we? > In fact, patch 2/2 of the series I sent earlier today has a similar side effect, by putting the HYP idmap before _stext. >>> Another question below: >>> >>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> >>>> --- >>>> arch/arm/kernel/vmlinux.lds.S | 12 +++++++++--- >>>> arch/arm/kvm/init.S | 11 +++++++++++ >>>> arch/arm/kvm/mmu.c | 42 +++++------------------------------------ >>>> arch/arm64/kernel/vmlinux.lds.S | 18 ++++++++++++------ >>>> 4 files changed, 37 insertions(+), 46 deletions(-) >>>> >>>> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S >>>> index b31aa73e8076..8179d3903dee 100644 >>>> --- a/arch/arm/kernel/vmlinux.lds.S >>>> +++ b/arch/arm/kernel/vmlinux.lds.S >>>> @@ -23,7 +23,7 @@ >>>> VMLINUX_SYMBOL(__idmap_text_start) = .; \ >>>> *(.idmap.text) \ >>>> VMLINUX_SYMBOL(__idmap_text_end) = .; \ >>>> - . = ALIGN(32); \ >>>> + . = ALIGN(1 << __hyp_idmap_align_order); \ >>>> VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \ >>>> *(.hyp.idmap.text) \ >>>> VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; >>>> @@ -346,8 +346,14 @@ SECTIONS >>>> */ >>>> ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support") >>>> ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined") >>>> + >>>> /* >>>> - * The HYP init code can't be more than a page long. >>>> + * The HYP init code can't be more than a page long, >>>> + * and should not cross a page boundary. >>>> * The above comment applies as well. >>>> */ >>>> -ASSERT(((__hyp_idmap_text_end - __hyp_idmap_text_start) <= PAGE_SIZE), "HYP init code too big") >>>> +ASSERT(((__hyp_idmap_text_end - 1) & PAGE_MASK) - >>>> + (__hyp_idmap_text_start & PAGE_MASK) == 0, >>>> + "HYP init code too big or unaligned") >>>> +ASSERT(__hyp_idmap_size <= (1 << __hyp_idmap_align_order), >>>> + "__hyp_idmap_size should be <= (1 << __hyp_idmap_align_order)") >>>> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S >>>> index 3988e72d16ff..7a279bc8e0e1 100644 >>>> --- a/arch/arm/kvm/init.S >>>> +++ b/arch/arm/kvm/init.S >>>> @@ -157,3 +157,14 @@ target: @ We're now in the trampoline code, switch page tables >>>> __kvm_hyp_init_end: >>>> >>>> .popsection >>>> + >>>> + /* >>>> + * When making changes to this file, make sure that the value of >>>> + * __hyp_idmap_align_order is updated if the size of the code ends up >>>> + * exceeding (1 << __hyp_idmap_align_order). This helps ensure that the >>>> + * code never crosses a page boundary, without wasting too much memory >>>> + * on aligning to PAGE_SIZE. >>>> + */ >>>> + .global __hyp_idmap_size, __hyp_idmap_align_order >>>> + .set __hyp_idmap_size, __kvm_hyp_init_end - __kvm_hyp_init >>>> + .set __hyp_idmap_align_order, 8 >>> >>> Is there a way to generate this __hyp_idmap_align_order automatically? >>> We're already pretty close to this 8 bit limit... >>> >> >> This seems to work: >> >> #define HYP_IDMAP_ALIGN \ >> __hyp_idmap_size <= 0x100 ? 0x100 : \ >> __hyp_idmap_size <= 0x200 ? 0x200 : \ >> __hyp_idmap_size <= 0x400 ? 0x400 : \ >> __hyp_idmap_size <= 0x800 ? 0x800 : 0x1000 >> >> and >> >> . = ALIGN(HYP_IDMAP_ALIGN); \ >> >> and we are limited at 1 page anyway. > > Ah, excellent. > >> Should I respin and include the move to RODATA at the same time? >> Or would you like me to rebase onto Arnd's patch? > > [adding Arnd on CC] > > Rebasing on top of Arnd's patch seems fair, as he came up with the idea > the first place. > OK, that's fine. @Arnd: I think you should move the ALIGN(32) along with the idmap bits into .rodata. Could you cc me on the updated patch? I will rebase this on top of it then. Thanks, Ard.
On 26 February 2015 at 18:41, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 26 February 2015 at 18:24, Marc Zyngier <marc.zyngier@arm.com> wrote: >> On 26/02/15 17:31, Ard Biesheuvel wrote: >>> On 26 February 2015 at 16:10, Marc Zyngier <marc.zyngier@arm.com> wrote: >>>> On 26/02/15 15:29, Ard Biesheuvel wrote: >>>>> The HYP init bounce page is a runtime construct that ensures that the >>>>> HYP init code does not cross a page boundary. However, this is something >>>>> we can do perfectly well at build time, by aligning the code appropriately. >>>>> >>>>> For arm64, we just align to 4 KB, and enforce that the code size is less >>>>> than 4 KB, regardless of the chosen page size. >>>>> >>>>> For ARM, the whole code is less than 256 bytes, so we tweak the linker >>>>> script to align at a power of 2 upper bound of the code size >>>>> >>>>> Note that this also fixes a benign off-by-one error in the original bounce >>>>> page code, where a bounce page would be allocated unnecessarily if the code >>>>> was exactly 1 page in size. >>>> >>>> I really like this simplification. Can you please check that it still >>>> work on 32bit with this patch from Arnd? >>>> >>>> https://www.mail-archive.com/kvm@vger.kernel.org/msg112364.html >>>> >>> >>> Yes, it does. >>> >>> Note that the kernel's RODATA permissions shouldn't affect whether >>> this code is executable or not in HYP mode, so I think this code >>> belongs in RODATA in the 1st place. >> >> Yup. Maybe we should do the same for arm64, shouldn't we? >> > > In fact, patch 2/2 of the series I sent earlier today has a similar > side effect, by putting the HYP idmap before _stext. > >>>> Another question below: >>>> >>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> >>>>> --- >>>>> arch/arm/kernel/vmlinux.lds.S | 12 +++++++++--- >>>>> arch/arm/kvm/init.S | 11 +++++++++++ >>>>> arch/arm/kvm/mmu.c | 42 +++++------------------------------------ >>>>> arch/arm64/kernel/vmlinux.lds.S | 18 ++++++++++++------ >>>>> 4 files changed, 37 insertions(+), 46 deletions(-) >>>>> >>>>> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S >>>>> index b31aa73e8076..8179d3903dee 100644 >>>>> --- a/arch/arm/kernel/vmlinux.lds.S >>>>> +++ b/arch/arm/kernel/vmlinux.lds.S >>>>> @@ -23,7 +23,7 @@ >>>>> VMLINUX_SYMBOL(__idmap_text_start) = .; \ >>>>> *(.idmap.text) \ >>>>> VMLINUX_SYMBOL(__idmap_text_end) = .; \ >>>>> - . = ALIGN(32); \ >>>>> + . = ALIGN(1 << __hyp_idmap_align_order); \ >>>>> VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \ >>>>> *(.hyp.idmap.text) \ >>>>> VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; >>>>> @@ -346,8 +346,14 @@ SECTIONS >>>>> */ >>>>> ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support") >>>>> ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined") >>>>> + >>>>> /* >>>>> - * The HYP init code can't be more than a page long. >>>>> + * The HYP init code can't be more than a page long, >>>>> + * and should not cross a page boundary. >>>>> * The above comment applies as well. >>>>> */ >>>>> -ASSERT(((__hyp_idmap_text_end - __hyp_idmap_text_start) <= PAGE_SIZE), "HYP init code too big") >>>>> +ASSERT(((__hyp_idmap_text_end - 1) & PAGE_MASK) - >>>>> + (__hyp_idmap_text_start & PAGE_MASK) == 0, >>>>> + "HYP init code too big or unaligned") >>>>> +ASSERT(__hyp_idmap_size <= (1 << __hyp_idmap_align_order), >>>>> + "__hyp_idmap_size should be <= (1 << __hyp_idmap_align_order)") >>>>> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S >>>>> index 3988e72d16ff..7a279bc8e0e1 100644 >>>>> --- a/arch/arm/kvm/init.S >>>>> +++ b/arch/arm/kvm/init.S >>>>> @@ -157,3 +157,14 @@ target: @ We're now in the trampoline code, switch page tables >>>>> __kvm_hyp_init_end: >>>>> >>>>> .popsection >>>>> + >>>>> + /* >>>>> + * When making changes to this file, make sure that the value of >>>>> + * __hyp_idmap_align_order is updated if the size of the code ends up >>>>> + * exceeding (1 << __hyp_idmap_align_order). This helps ensure that the >>>>> + * code never crosses a page boundary, without wasting too much memory >>>>> + * on aligning to PAGE_SIZE. >>>>> + */ >>>>> + .global __hyp_idmap_size, __hyp_idmap_align_order >>>>> + .set __hyp_idmap_size, __kvm_hyp_init_end - __kvm_hyp_init >>>>> + .set __hyp_idmap_align_order, 8 >>>> >>>> Is there a way to generate this __hyp_idmap_align_order automatically? >>>> We're already pretty close to this 8 bit limit... >>>> >>> >>> This seems to work: >>> >>> #define HYP_IDMAP_ALIGN \ >>> __hyp_idmap_size <= 0x100 ? 0x100 : \ >>> __hyp_idmap_size <= 0x200 ? 0x200 : \ >>> __hyp_idmap_size <= 0x400 ? 0x400 : \ >>> __hyp_idmap_size <= 0x800 ? 0x800 : 0x1000 >>> >>> and >>> >>> . = ALIGN(HYP_IDMAP_ALIGN); \ >>> >>> and we are limited at 1 page anyway. >> >> Ah, excellent. >> >>> Should I respin and include the move to RODATA at the same time? >>> Or would you like me to rebase onto Arnd's patch? >> >> [adding Arnd on CC] >> >> Rebasing on top of Arnd's patch seems fair, as he came up with the idea >> the first place. >> > > OK, that's fine. > > @Arnd: I think you should move the ALIGN(32) along with the idmap bits > into .rodata. > Could you cc me on the updated patch? I will rebase this on top of it then. Actually, it makes much more sense for me just to update the patch and resend it, so that is what I am about to do.
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S index b31aa73e8076..8179d3903dee 100644 --- a/arch/arm/kernel/vmlinux.lds.S +++ b/arch/arm/kernel/vmlinux.lds.S @@ -23,7 +23,7 @@ VMLINUX_SYMBOL(__idmap_text_start) = .; \ *(.idmap.text) \ VMLINUX_SYMBOL(__idmap_text_end) = .; \ - . = ALIGN(32); \ + . = ALIGN(1 << __hyp_idmap_align_order); \ VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \ *(.hyp.idmap.text) \ VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; @@ -346,8 +346,14 @@ SECTIONS */ ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support") ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined") + /* - * The HYP init code can't be more than a page long. + * The HYP init code can't be more than a page long, + * and should not cross a page boundary. * The above comment applies as well. */ -ASSERT(((__hyp_idmap_text_end - __hyp_idmap_text_start) <= PAGE_SIZE), "HYP init code too big") +ASSERT(((__hyp_idmap_text_end - 1) & PAGE_MASK) - + (__hyp_idmap_text_start & PAGE_MASK) == 0, + "HYP init code too big or unaligned") +ASSERT(__hyp_idmap_size <= (1 << __hyp_idmap_align_order), + "__hyp_idmap_size should be <= (1 << __hyp_idmap_align_order)") diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S index 3988e72d16ff..7a279bc8e0e1 100644 --- a/arch/arm/kvm/init.S +++ b/arch/arm/kvm/init.S @@ -157,3 +157,14 @@ target: @ We're now in the trampoline code, switch page tables __kvm_hyp_init_end: .popsection + + /* + * When making changes to this file, make sure that the value of + * __hyp_idmap_align_order is updated if the size of the code ends up + * exceeding (1 << __hyp_idmap_align_order). This helps ensure that the + * code never crosses a page boundary, without wasting too much memory + * on aligning to PAGE_SIZE. + */ + .global __hyp_idmap_size, __hyp_idmap_align_order + .set __hyp_idmap_size, __kvm_hyp_init_end - __kvm_hyp_init + .set __hyp_idmap_align_order, 8 diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index 3e6859bc3e11..42a24d6b003b 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -37,7 +37,6 @@ static pgd_t *boot_hyp_pgd; static pgd_t *hyp_pgd; static DEFINE_MUTEX(kvm_hyp_pgd_mutex); -static void *init_bounce_page; static unsigned long hyp_idmap_start; static unsigned long hyp_idmap_end; static phys_addr_t hyp_idmap_vector; @@ -405,9 +404,6 @@ void free_boot_hyp_pgd(void) if (hyp_pgd) unmap_range(NULL, hyp_pgd, TRAMPOLINE_VA, PAGE_SIZE); - free_page((unsigned long)init_bounce_page); - init_bounce_page = NULL; - mutex_unlock(&kvm_hyp_pgd_mutex); } @@ -1498,39 +1494,11 @@ int kvm_mmu_init(void) hyp_idmap_end = kvm_virt_to_phys(__hyp_idmap_text_end); hyp_idmap_vector = kvm_virt_to_phys(__kvm_hyp_init); - if ((hyp_idmap_start ^ hyp_idmap_end) & PAGE_MASK) { - /* - * Our init code is crossing a page boundary. Allocate - * a bounce page, copy the code over and use that. - */ - size_t len = __hyp_idmap_text_end - __hyp_idmap_text_start; - phys_addr_t phys_base; - - init_bounce_page = (void *)__get_free_page(GFP_KERNEL); - if (!init_bounce_page) { - kvm_err("Couldn't allocate HYP init bounce page\n"); - err = -ENOMEM; - goto out; - } - - memcpy(init_bounce_page, __hyp_idmap_text_start, len); - /* - * Warning: the code we just copied to the bounce page - * must be flushed to the point of coherency. - * Otherwise, the data may be sitting in L2, and HYP - * mode won't be able to observe it as it runs with - * caches off at that point. - */ - kvm_flush_dcache_to_poc(init_bounce_page, len); - - phys_base = kvm_virt_to_phys(init_bounce_page); - hyp_idmap_vector += phys_base - hyp_idmap_start; - hyp_idmap_start = phys_base; - hyp_idmap_end = phys_base + len; - - kvm_info("Using HYP init bounce page @%lx\n", - (unsigned long)phys_base); - } + /* + * We rely on the linker script to ensure at build time that the HYP + * init code does not cross a page boundary. + */ + BUG_ON((hyp_idmap_start ^ (hyp_idmap_end - 1)) & PAGE_MASK); hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, hyp_pgd_order); boot_hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, hyp_pgd_order); diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 5d9d2dca530d..17383c257a7d 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -23,10 +23,14 @@ jiffies = jiffies_64; #define HYPERVISOR_TEXT \ /* \ - * Force the alignment to be compatible with \ - * the vectors requirements \ + * Align to 4K so that \ + * a) the HYP vector table is at its minimum \ + * alignment of 2048 bytes \ + * b) the HYP init code will not cross a page \ + * boundary if its size does not exceed \ + * 4K (see related ASSERT() below) \ */ \ - . = ALIGN(2048); \ + . = ALIGN(SZ_4K); \ VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \ *(.hyp.idmap.text) \ VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; \ @@ -163,10 +167,12 @@ SECTIONS } /* - * The HYP init code can't be more than a page long. + * The HYP init code can't be more than a page long, + * and should not cross a page boundary. */ -ASSERT(((__hyp_idmap_text_start + PAGE_SIZE) > __hyp_idmap_text_end), - "HYP init code too big") +ASSERT(((__hyp_idmap_text_end - 1) & ~(SZ_4K - 1)) - + (__hyp_idmap_text_start & ~(SZ_4K - 1)) == 0, + "HYP init code too big or unaligned") /* * If padding is applied before .head.text, virt<->phys conversions will fail.
The HYP init bounce page is a runtime construct that ensures that the HYP init code does not cross a page boundary. However, this is something we can do perfectly well at build time, by aligning the code appropriately. For arm64, we just align to 4 KB, and enforce that the code size is less than 4 KB, regardless of the chosen page size. For ARM, the whole code is less than 256 bytes, so we tweak the linker script to align at a power of 2 upper bound of the code size Note that this also fixes a benign off-by-one error in the original bounce page code, where a bounce page would be allocated unnecessarily if the code was exactly 1 page in size. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm/kernel/vmlinux.lds.S | 12 +++++++++--- arch/arm/kvm/init.S | 11 +++++++++++ arch/arm/kvm/mmu.c | 42 +++++------------------------------------ arch/arm64/kernel/vmlinux.lds.S | 18 ++++++++++++------ 4 files changed, 37 insertions(+), 46 deletions(-)