linux-kernel - Re: [RFC PATCH v2 24/26] KVM: arm64: Make memcache anonymous in pgtable allocator

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Message-ID: <20210203155944.GH18974@willie-the-truck>
Date:   Wed, 3 Feb 2021 15:59:44 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, android-kvm@...gle.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Fuad Tabba <tabba@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>
Subject: Re: [RFC PATCH v2 24/26] KVM: arm64: Make memcache anonymous in
 pgtable allocator

On Fri, Jan 08, 2021 at 12:15:22PM +0000, Quentin Perret wrote:
> The current stage2 page-table allocator uses a memcache to get
> pre-allocated pages when it needs any. To allow re-using this code at
> EL2 which uses a concept of memory pools, make the memcache argument to
> kvm_pgtable_stage2_map() anonymous. and let the mm_ops zalloc_page()
> callbacks use it the way they need to.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 6 +++---
>  arch/arm64/kvm/hyp/pgtable.c         | 4 ++--
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 8e8f1d2c5e0e..d846bc3d3b77 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -176,8 +176,8 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
>   * @size:	Size of the mapping.
>   * @phys:	Physical address of the memory to map.
>   * @prot:	Permissions and attributes for the mapping.
> - * @mc:		Cache of pre-allocated GFP_PGTABLE_USER memory from which to
> - *		allocate page-table pages.
> + * @mc:		Cache of pre-allocated memory from which to allocate page-table
> + *		pages.

We should probably mention that this memory must be zeroed, since I don't
think the page-table code takes care of that.

Will