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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Jia He <justin.he@arm.com>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"James Morse" <james.morse@arm.com>,
	"Marc Zyngier" <maz@kernel.org>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	"Punit Agrawal" <punitagrawal@gmail.com>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Jun Yao" <yaojun8558363@gmail.com>,
	"Alex Van Brunt" <avanbrunt@nvidia.com>,
	"Robin Murphy" <robin.murphy@arm.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Ralph Campbell" <rcampbell@nvidia.com>,
	hejianet@gmail.com
Subject: Re: [PATCH v3 1/2] arm64: mm: implement arch_faults_on_old_pte() on arm64
Date: Mon, 16 Sep 2019 12:20:37 +0300
Message-ID: <20190916092037.yqdp2vyhl4byhbh5@box.shutemov.name> (raw)
In-Reply-To: <20190913163239.125108-2-justin.he@arm.com>

On Sat, Sep 14, 2019 at 12:32:38AM +0800, Jia He wrote:
> On arm64 without hardware Access Flag, copying fromuser will fail because
> the pte is old and cannot be marked young. So we always end up with zeroed
> page after fork() + CoW for pfn mappings. we don't always have a
> hardware-managed access flag on arm64.
> 
> Hence implement arch_faults_on_old_pte on arm64 to indicate that it might
> cause page fault when accessing old pte.
> 
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
>  arch/arm64/include/asm/pgtable.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index e09760ece844..b41399d758df 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -868,6 +868,18 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
>  #define phys_to_ttbr(addr)	(addr)
>  #endif
>  
> +/*
> + * On arm64 without hardware Access Flag, copying fromuser will fail because
> + * the pte is old and cannot be marked young. So we always end up with zeroed
> + * page after fork() + CoW for pfn mappings. we don't always have a
> + * hardware-managed access flag on arm64.
> + */
> +static inline bool arch_faults_on_old_pte(void)
> +{
> +	return true;

Shouldn't youc check if this particular machine supports hardware access
bit?

> +}
> +#define arch_faults_on_old_pte arch_faults_on_old_pte
> +
>  #endif /* !__ASSEMBLY__ */
>  
>  #endif /* __ASM_PGTABLE_H */
> -- 
> 2.17.1
> 
> 

-- 
 Kirill A. Shutemov


  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-13 16:32 [PATCH v3 0/2] fix double page fault " Jia He
2019-09-13 16:32 ` [PATCH v3 1/2] arm64: mm: implement arch_faults_on_old_pte() " Jia He
2019-09-16  9:20   ` Kirill A. Shutemov [this message]
2019-09-13 16:32 ` [PATCH v3 2/2] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-16  9:16   ` Kirill A. Shutemov
2019-09-16  9:35     ` Justin He (Arm Technology China)
2019-09-16 14:16       ` Kirill A. Shutemov

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