[PATCH 1/1] arch/arm/mm: fix major fault accounting when retrying under per-VMA lock

[PATCH 1/1] arch/arm/mm: fix major fault accounting when retrying under per-VMA lock

[Suren Baghdasaryan]

The change [1] missed ARM architecture when fixing major fault accounting
for page fault retry under per-VMA lock. Add missing code to fix ARM
architecture fault accounting.

[1] 46e714c729c8 ("arch/mm/fault: fix major fault accounting when retrying under per-VMA lock")

Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock")

Reported-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 arch/arm/mm/fault.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index e96fb40b9cc3..07565b593ed6 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -298,6 +298,8 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *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)) {
-- 
2.43.0.429.g432eaa2c6b-goog

Re: [PATCH 1/1] arch/arm/mm: fix major fault accounting when retrying under per-VMA lock

[Andrew Morton]

On Mon, 22 Jan 2024 22:43:05 -0800 Suren Baghdasaryan <surenb@google.com> wrote:

> The change [1] missed ARM architecture when fixing major fault accounting
> for page fault retry under per-VMA lock. Add missing code to fix ARM
> architecture fault accounting.
> 
> [1] 46e714c729c8 ("arch/mm/fault: fix major fault accounting when retrying under per-VMA lock")
> 
> Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock")

What are the userspace-visible runtime effects of this change?

Is a cc:stable backport desirable?

> Reported-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Re: [PATCH 1/1] arch/arm/mm: fix major fault accounting when retrying under per-VMA lock

[Suren Baghdasaryan]

On Thu, Jan 25, 2024 at 6:04 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 22 Jan 2024 22:43:05 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
>
> > The change [1] missed ARM architecture when fixing major fault accounting
> > for page fault retry under per-VMA lock. Add missing code to fix ARM
> > architecture fault accounting.
> >
> > [1] 46e714c729c8 ("arch/mm/fault: fix major fault accounting when retrying under per-VMA lock")
> >
> > Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock")
>
> What are the userspace-visible runtime effects of this change?

The user-visible effects is that it restores correct major fault
accounting that was broken after [2] was merged in 6.7 kernel. The
more detailed description is in [3] and this patch simply adds the
same fix to ARM architecture which I missed in [3]. I can re-send the
patch with the full description from [3] if needed.

>
> Is a cc:stable backport desirable?

Yes, I guess since [2] was merged in 6.7, cc-ing stable would be desirable.
Please let me know if you want me to re-send the patch with full
description and CC'ing stable.

[2] https://lore.kernel.org/all/20231006195318.4087158-6-willy@infradead.org/
[3] https://lore.kernel.org/all/20231226214610.109282-1-surenb@google.com/

>
> > Reported-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Re: [PATCH 1/1] arch/arm/mm: fix major fault accounting when retrying under per-VMA lock

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (fixes)
by Andrew Morton <akpm@linux-foundation.org>:

On Mon, 22 Jan 2024 22:43:05 -0800 you wrote:
> The change [1] missed ARM architecture when fixing major fault accounting
> for page fault retry under per-VMA lock. Add missing code to fix ARM
> architecture fault accounting.
> 
> [1] 46e714c729c8 ("arch/mm/fault: fix major fault accounting when retrying under per-VMA lock")
> 
> Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock")
> 
> [...]

Here is the summary with links:
  - [1/1] arch/arm/mm: fix major fault accounting when retrying under per-VMA lock
    https://git.kernel.org/riscv/c/e870920bbe68

You are awesome, thank you!
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