linux-kernel - Re: [PATCH v6 1/4] KVM: arm64: Introduce cache maintenance callbacks for guest stage-2

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Message-ID: <CA+EHjTyVnHkk5rYb=W6msqoT5E_bVTBdhLtpeRR_b2wsib4Vgw@mail.gmail.com>
Date:   Fri, 18 Jun 2021 09:50:06 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Yanan Wang <wangyanan55@...wei.com>
Cc:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v6 1/4] KVM: arm64: Introduce cache maintenance callbacks
 for guest stage-2

Hi Yanan,

On Wed, Jun 16, 2021 at 10:52 AM Yanan Wang <wangyanan55@...wei.com> wrote:
>
> To prepare for performing guest CMOs in the fault handlers in pgtable.c,
> introduce two cache maintenance callbacks in struct kvm_pgtable_mm_ops.
>
> The new callbacks are specific for guest stage-2, so they will only be
> initialized in 'struct kvm_pgtable_mm_ops kvm_s2_mm_ops'.
>
> Signed-off-by: Yanan Wang <wangyanan55@...wei.com>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index c3674c47d48c..302eca32e0af 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -44,6 +44,11 @@ typedef u64 kvm_pte_t;
>   *                     in the current context.
>   * @virt_to_phys:      Convert a virtual address mapped in the current context
>   *                     into a physical address.
> + * @flush_dcache:      Clean data cache for a guest page address range before
> + *                     creating the corresponding stage-2 mapping.
> + * @flush_icache:      Invalidate instruction cache for a guest page address
> + *                     range before creating or updating the corresponding
> + *                     stage-2 mapping.
>   */
>  struct kvm_pgtable_mm_ops {
>         void*           (*zalloc_page)(void *arg);
> @@ -54,6 +59,8 @@ struct kvm_pgtable_mm_ops {
>         int             (*page_count)(void *addr);
>         void*           (*phys_to_virt)(phys_addr_t phys);
>         phys_addr_t     (*virt_to_phys)(void *addr);
> +       void            (*flush_dcache)(void *addr, size_t size);
> +       void            (*flush_icache)(void *addr, size_t size);
>  };
>

Just to add to Marc's comment on naming, flush_dcache is in this case
a clean and invalidate: I see that in patch 4 it eventually does a
civac. So, yes, although it is a mouthful, I think it should be
dcache_clean_inval and not just dcache_clean. An alternative, if it's
acceptable by Marc and the others, is to name the parameters dcmo/icmo
or something like that, where the nature of the maintenance operation
is not necessarily tied to the name.

For reference, this is the patch Marc mentioned, where we're trying to
fix the naming to make it consistent with Arm terminology (Arm doesn't
define what a flush is):
https://lore.kernel.org/linux-arm-kernel/20210524083001.2586635-19-tabba@google.com/

Otherwise:
Reviewed-by: Fuad Tabba <tabba@...gle.com>

Cheers,
/fuad

>  /**
> --
> 2.23.0
>
> _______________________________________________
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> kvmarm@...ts.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

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