linux-kernel - [PATCH] arm64: mm: pass original fault address to handle_mm_fault() in PER_VMA

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Date:   Wed, 24 May 2023 21:13:05 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Suren Baghdasaryan <surenb@...gle.com>
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 <jszhang@...nel.org>
---
 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