From: Will Deacon <will@kernel.org>
To: Jia He <justin.he@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
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>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
hejianet@gmail.com, Kaly Xin <Kaly.Xin@arm.com>
Subject: Re: [PATCH v10 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64
Date: Tue, 1 Oct 2019 13:50:32 +0100 [thread overview]
Message-ID: <20191001125031.7ddm5dlwss6m3dth@willie-the-truck> (raw)
In-Reply-To: <20190930015740.84362-3-justin.he@arm.com>
On Mon, Sep 30, 2019 at 09:57:39AM +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>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> ---
> arch/arm64/include/asm/pgtable.h | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 7576df00eb50..e96fb82f62de 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -885,6 +885,20 @@ 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 from user 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)
> +{
> + WARN_ON(preemptible());
> +
> + return !cpu_has_hw_af();
> +}
Does this work correctly in a KVM guest? (i.e. is the MMFR sanitised in that
case, despite not being the case on the host?)
Will
next prev parent reply other threads:[~2019-10-01 12:50 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-30 1:57 [PATCH v10 0/3] fix double page fault on arm64 Jia He
2019-09-30 1:57 ` [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-10-01 12:54 ` Will Deacon
2019-10-01 13:18 ` Marc Zyngier
2019-10-08 1:12 ` Justin He (Arm Technology China)
2019-10-08 15:32 ` Suzuki K Poulose
2019-10-09 6:29 ` Jia He
2019-09-30 1:57 ` [PATCH v10 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-10-01 12:50 ` Will Deacon [this message]
2019-10-01 13:32 ` Marc Zyngier
2019-10-08 1:55 ` Justin He (Arm Technology China)
2019-10-08 2:30 ` Justin He (Arm Technology China)
2019-10-08 7:46 ` Marc Zyngier
2019-09-30 1:57 ` [PATCH v10 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-10-01 12:54 ` Will Deacon
2019-10-08 2:19 ` Justin He (Arm Technology China)
2019-10-08 12:39 ` Will Deacon
2019-10-08 12:58 ` Justin He (Arm Technology China)
2019-10-08 14:32 ` Kirill A. Shutemov
2019-10-16 23:21 ` Palmer Dabbelt
2019-10-16 23:46 ` Will Deacon
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