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* Re: [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks
@ 2015-12-16  3:01 Andrew Pinski
  2015-12-16 11:15   ` James Morse
  0 siblings, 1 reply; 4+ messages in thread
From: Andrew Pinski @ 2015-12-16  3:01 UTC (permalink / raw)
  To: Catalin Marinas, LKML
  Cc: linux-arm-kernel@lists.infradead.org, Andrew Pinski, Ming Lei,
	Will Deacon, David Daney

On Tue, Dec 9, 2015 at 17:26:56, Catalin Marinas
<catalin.marinas@arm.com> wrote:
>
> Currently the BUG_ON() checks do not give enough information about the PTEs being set. This patch changes BUG_ON to WARN_ONCE and dumps the values of the old and new PTEs.


This change broke building the mantis driver:

In file included from ./arch/arm64/include/asm/io.h:30:0,
                 from drivers/media/pci/mantis/mantis_i2c.c:21:
./arch/arm64/include/asm/pgtable.h: In function ‘set_pte_at’:
./arch/arm64/include/asm/pgtable.h:281:3: error: implicit declaration
of function ‘BUILD_BUG_ON_INVALID’
[-Werror=implicit-function-declaration]
   VM_WARN_ONCE(!pte_young(pte),
   ^

Thanks,
Andrew Pinski

>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
>   arch/arm64/include/asm/pgtable.h | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h
> b/arch/arm64/include/asm/pgtable.h
> index 7e074f93f383..002dc61a4dff 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -276,10 +276,13 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
>          * hardware updates of the pte (ptep_set_access_flags safely changes
>          * valid ptes without going through an invalid entry).
>          */
> -       if (IS_ENABLED(CONFIG_DEBUG_VM) && IS_ENABLED(CONFIG_ARM64_HW_AFDBM) &&
> -           pte_valid(*ptep)) {
> -               BUG_ON(!pte_young(pte));
> -               BUG_ON(pte_write(*ptep) && !pte_dirty(pte));
> +       if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && pte_valid(*ptep)) {
> +               VM_WARN_ONCE(!pte_young(pte),
> +                            "%s: racy access flag clearing: %016llx -> %016llx",
> +                            __func__, pte_val(*ptep), pte_val(pte));
> +               VM_WARN_ONCE(pte_write(*ptep) && !pte_dirty(pte),
> +                            "%s: racy dirty state clearing: %016llx -> %016llx",
> +                            __func__, pte_val(*ptep), pte_val(pte));
>         }
>
>         set_pte(ptep, pte);
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
>
>
>

^ permalink raw reply	[flat|nested] 4+ messages in thread
* [PATCH 0/2] arm64: Non-racy PTE setting in the presence of HW AF/DBM
@ 2015-12-09 17:26 Catalin Marinas
  2015-12-09 17:26 ` [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks Catalin Marinas
  0 siblings, 1 reply; 4+ messages in thread
From: Catalin Marinas @ 2015-12-09 17:26 UTC (permalink / raw)
  To: linux-arm-kernel

This series addresses a potentially racy default implementation of
ptep_set_access_flags() when hardware update of the access or dirty
states is enabled. The first patch is some clean-up in set_pte_at() to
improve the information reporting and replace BUG with WARN. The second
patch contains the arm64-specific ptep_set_access_flags()
implementation.

Possible racy scenarios are described in patch 2. I think this series
could be simplified on the following assumptions:

a) if the CPUs do not support HW AF/DBM or it is disabled, no other
   agent in the system will perform such updates

b) if one CPU supports HW AF/DBM, all of them must do (don't mix such
   features)

Point (a) means that the current code works fine and BUG_ON() is not
necessary.

Point (b) however requires a ptep_set_access_flags() similar to the x86
one, i.e. only do the setting if (changed && dirty), otherwise let the
hardware handle the updates.

Anyway, while patch 2 is still debatable, I'd like to merge the first
patch in 4.4 to avoid an unnecessary BUG_ON on hardware that doesn't
even do DBM.

Catalin


Catalin Marinas (2):
  arm64: Improve error reporting on set_pte_at() checks
  arm64: Implement ptep_set_access_flags() for hardware AF/DBM

 arch/arm64/include/asm/pgtable.h | 16 ++++++++---
 arch/arm64/mm/fault.c            | 57 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 4 deletions(-)

^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2015-12-16 11:16 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2015-12-16  3:01 [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks Andrew Pinski
2015-12-16 11:15 ` James Morse
2015-12-16 11:15   ` James Morse
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2015-12-09 17:26 [PATCH 0/2] arm64: Non-racy PTE setting in the presence of HW AF/DBM Catalin Marinas
2015-12-09 17:26 ` [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks Catalin Marinas

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