2023-05-24 13:30:26

by Jisheng Zhang

Subject: [PATCH] arm64: mm: pass original fault address to handle_mm_fault() in PER_VMA_LOCK block

When reading the arm64's PER_VMA_LOCK support code, I found a bit
difference between arm64 and other arch when calling handle_mm_fault()
during VMA lock-based page fault handling: the fault address is masked
before passing to handle_mm_fault(). This is also different from the
usage in mmap_lock-based handling. I think we need to pass the
original fault address to handle_mm_fault() as we did in
commit 84c5e23edecd ("arm64: mm: Pass original fault address to
handle_mm_fault()").

If we go through the code path further, we can find that the "masked"
fault address can cause mismatched fault address between perf sw
major/minor page fault sw event and perf page fault sw event:

do_page_fault
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, ..., addr) // orig addr
handle_mm_fault
mm_account_fault
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, ...) // masked addr

Fixes: cd7f176aea5f ("arm64/mm: try VMA lock-based page fault handling first")
Signed-off-by: Jisheng Zhang <[email protected]>
---
arch/arm64/mm/fault.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index cb21ccd7940d..6045a5117ac1 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -600,8 +600,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
vma_end_read(vma);
goto lock_mmap;
}
- fault = handle_mm_fault(vma, addr & PAGE_MASK,
- mm_flags | FAULT_FLAG_VMA_LOCK, regs);
+ fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs);
vma_end_read(vma);

if (!(fault & VM_FAULT_RETRY)) {
--
2.40.1

2023-05-25 17:23:05

by Catalin Marinas

Subject: Re: [PATCH] arm64: mm: pass original fault address to handle_mm_fault() in PER_VMA_LOCK block

On Wed, May 24, 2023 at 09:13:05PM +0800, Jisheng Zhang wrote:
> When reading the arm64's PER_VMA_LOCK support code, I found a bit
> difference between arm64 and other arch when calling handle_mm_fault()
> during VMA lock-based page fault handling: the fault address is masked
> before passing to handle_mm_fault(). This is also different from the
> usage in mmap_lock-based handling. I think we need to pass the
> original fault address to handle_mm_fault() as we did in
> commit 84c5e23edecd ("arm64: mm: Pass original fault address to
> handle_mm_fault()").
>
> If we go through the code path further, we can find that the "masked"
> fault address can cause mismatched fault address between perf sw
> major/minor page fault sw event and perf page fault sw event:
>
> do_page_fault
> perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, ..., addr) // orig addr
> handle_mm_fault
> mm_account_fault
> perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, ...) // masked addr
>
> Fixes: cd7f176aea5f ("arm64/mm: try VMA lock-based page fault handling first")
> Signed-off-by: Jisheng Zhang <[email protected]>

Acked-by: Catalin Marinas <[email protected]>

2023-06-02 12:43:13

by Will Deacon

Subject: Re: [PATCH] arm64: mm: pass original fault address to handle_mm_fault() in PER_VMA_LOCK block

On Wed, 24 May 2023 21:13:05 +0800, Jisheng Zhang wrote:
> When reading the arm64's PER_VMA_LOCK support code, I found a bit
> difference between arm64 and other arch when calling handle_mm_fault()
> during VMA lock-based page fault handling: the fault address is masked
> before passing to handle_mm_fault(). This is also different from the
> usage in mmap_lock-based handling. I think we need to pass the
> original fault address to handle_mm_fault() as we did in
> commit 84c5e23edecd ("arm64: mm: Pass original fault address to
> handle_mm_fault()").
>
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: mm: pass original fault address to handle_mm_fault() in PER_VMA_LOCK block
https://git.kernel.org/arm64/c/0e2aba694866

Cheers,
--
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev