The patch titled
Subject: arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
Date: Tue, 26 Dec 2023 13:46:10 -0800
A test [1] in Android test suite started failing after [2] was merged. It
turns out that after handling a major fault under per-VMA lock, the
process major fault counter does not register that fault as major. Before
[2] read faults would be done under mmap_lock, in which case
FAULT_FLAG_TRIED flag is set before retrying. That in turn causes
mm_account_fault() to account the fault as major once retry completes.
With per-VMA locks we often retry because a fault can't be handled without
locking the whole mm using mmap_lock. Therefore such retries do not set
FAULT_FLAG_TRIED flag. This logic does not work after [2] because we can
now handle read major faults under per-VMA lock and upon retry the fact
there was a major fault gets lost. Fix this by setting FAULT_FLAG_TRIED
after retrying under per-VMA lock if VM_FAULT_MAJOR was returned. Ideally
we would use an additional VM_FAULT bit to indicate the reason for the
retry (could not handle under per-VMA lock vs other reason) but this
simpler solution seems to work, so keeping it simple.
[1] https://cs.android.com/android/platform/superproject/+/master:test/vts-testcase/kernel/api/drop_caches_prop/drop_caches_test.cpp
[2] https://lore.kernel.org/all/20231006195318.4087158-6-willy@xxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20231226214610.109282-1-surenb@xxxxxxxxxx
Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock")
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/arm64/mm/fault.c | 2 ++
arch/powerpc/mm/fault.c | 2 ++
arch/riscv/mm/fault.c | 2 ++
arch/s390/mm/fault.c | 3 +++
arch/x86/mm/fault.c | 2 ++
5 files changed, 11 insertions(+)
--- a/arch/arm64/mm/fault.c~arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock
+++ a/arch/arm64/mm/fault.c
@@ -607,6 +607,8 @@ static int __kprobes do_page_fault(unsig
goto done;
}
count_vm_vma_lock_event(VMA_LOCK_RETRY);
+ if (fault & VM_FAULT_MAJOR)
+ mm_flags |= FAULT_FLAG_TRIED;
/* Quick path to respond to signals */
if (fault_signal_pending(fault, regs)) {
--- a/arch/powerpc/mm/fault.c~arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock
+++ a/arch/powerpc/mm/fault.c
@@ -497,6 +497,8 @@ static int ___do_page_fault(struct pt_re
goto done;
}
count_vm_vma_lock_event(VMA_LOCK_RETRY);
+ if (fault & VM_FAULT_MAJOR)
+ flags |= FAULT_FLAG_TRIED;
if (fault_signal_pending(fault, regs))
return user_mode(regs) ? 0 : SIGBUS;
--- a/arch/riscv/mm/fault.c~arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock
+++ a/arch/riscv/mm/fault.c
@@ -304,6 +304,8 @@ void handle_page_fault(struct pt_regs *r
goto done;
}
count_vm_vma_lock_event(VMA_LOCK_RETRY);
+ if (fault & VM_FAULT_MAJOR)
+ flags |= FAULT_FLAG_TRIED;
if (fault_signal_pending(fault, regs)) {
if (!user_mode(regs))
--- a/arch/s390/mm/fault.c~arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock
+++ a/arch/s390/mm/fault.c
@@ -337,6 +337,9 @@ static void do_exception(struct pt_regs
return;
}
count_vm_vma_lock_event(VMA_LOCK_RETRY);
+ if (fault & VM_FAULT_MAJOR)
+ flags |= FAULT_FLAG_TRIED;
+
/* Quick path to respond to signals */
if (fault_signal_pending(fault, regs)) {
if (!user_mode(regs))
--- a/arch/x86/mm/fault.c~arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock
+++ a/arch/x86/mm/fault.c
@@ -1370,6 +1370,8 @@ void do_user_addr_fault(struct pt_regs *
goto done;
}
count_vm_vma_lock_event(VMA_LOCK_RETRY);
+ if (fault & VM_FAULT_MAJOR)
+ flags |= FAULT_FLAG_TRIED;
/* Quick path to respond to signals */
if (fault_signal_pending(fault, regs)) {
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
arch-mm-fault-fix-major-fault-accounting-when-retrying-under-per-vma-lock.patch
selftests-mm-call-uffd_test_ctx_clear-at-the-end-of-the-test.patch
selftests-mm-add-uffd_test_case_ops-to-allow-test-case-specific-operations.patch
selftests-mm-add-uffdio_move-ioctl-test.patch
