linux-kernel - Re: [PATCH v6 02/11] KVM: arm64: Use kvm_arch_flush_remote

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Message-ID: <ef2dddcd-f4dd-da9b-c03f-ccd852bb8543@linaro.org>
Date:   Mon, 17 Jul 2023 10:12:57 +0200
From:   Philippe Mathieu-Daudé <philmd@...aro.org>
To:     Raghavendra Rao Ananta <rananta@...gle.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Jing Zhang <jingzhangos@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Zenghui Yu <zenghui.yu@...ux.dev>,
        Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v6 02/11] KVM: arm64: Use kvm_arch_flush_remote_tlbs()

Hi Raghavendra, David,

On 15/7/23 02:53, Raghavendra Rao Ananta wrote:
> From: David Matlack <dmatlack@...gle.com>
> 
> Use kvm_arch_flush_remote_tlbs() instead of
> CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL. The two mechanisms solve the same
> problem, allowing architecture-specific code to provide a non-IPI
> implementation of remote TLB flushing.
> 
> Dropping CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL allows KVM to standardize
> all architectures on kvm_arch_flush_remote_tlbs() instead of maintaining
> two mechanisms.
> 
> Opt to standardize on kvm_arch_flush_remote_tlbs() since it avoids
> duplicating the generic TLB stats across architectures that implement
> their own remote TLB flush.
> 
> This adds an extra function call to the ARM64 kvm_flush_remote_tlbs()
> path, but that is a small cost in comparison to flushing remote TLBs.
> 
> In addition, instead of just incrementing remote_tlb_flush_requests
> stat, the generic interface would also increment the
> remote_tlb_flush stat.
> 
> Signed-off-by: David Matlack <dmatlack@...gle.com>
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> Reviewed-by: Zenghui Yu <zenghui.yu@...ux.dev>
> Acked-by: Oliver Upton <oliver.upton@...ux.dev>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> ---
>   arch/arm64/include/asm/kvm_host.h | 3 +++
>   arch/arm64/kvm/Kconfig            | 1 -
>   arch/arm64/kvm/mmu.c              | 6 +++---
>   virt/kvm/Kconfig                  | 3 ---
>   virt/kvm/kvm_main.c               | 2 --
>   5 files changed, 6 insertions(+), 9 deletions(-)

You are doing 2 changes in the same patch:

- Have ARM use kvm_arch_flush_remote_tlbs() instead of
   HAVE_KVM_ARCH_TLB_FLUSH_ALL,
- Drop the now unused HAVE_KVM_ARCH_TLB_FLUSH_ALL.

Commits should be atomic, to allow partial
revert or cherry-pick.

Preferably splitting this patch in 2:
Reviewed-by: Philippe Mathieu-Daudé <philmd@...aro.org>

Regards,

Phil.