linux-kernel - Re: [PATCH 1/2] KVM: x86/mmu: Skip tlb flush if it has been done in zap_gfn

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Date:   Wed, 17 Nov 2021 15:56:00 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Hou Wenlong <houwenlong93@...ux.alibaba.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: x86/mmu: Skip tlb flush if it has been done in
 zap_gfn_range()

On Wed, Nov 17, 2021, Hou Wenlong wrote:
> If the parameter flush is set, zap_gfn_range() would flush remote tlb
> when yield, then tlb flush is not needed outside. So use the return
> value of zap_gfn_range() directly instead of OR on it in
> kvm_unmap_gfn_range() and kvm_tdp_mmu_unmap_gfn_range().
> 
> Fixes: 3039bcc744980 ("KVM: Move x86's MMU notifier memslot walkers to generic code")
> Signed-off-by: Hou Wenlong <houwenlong93@...ux.alibaba.com>
> ---

Ha, I fixed this in my local repo just yesterday :-)

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

>  arch/x86/kvm/mmu/mmu.c     | 2 +-
>  arch/x86/kvm/mmu/tdp_mmu.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 354d2ca92df4..d57319e596a9 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1582,7 +1582,7 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>  		flush = kvm_handle_gfn_range(kvm, range, kvm_unmap_rmapp);
>  
>  	if (is_tdp_mmu_enabled(kvm))
> -		flush |= kvm_tdp_mmu_unmap_gfn_range(kvm, range, flush);
> +		flush = kvm_tdp_mmu_unmap_gfn_range(kvm, range, flush);
>  
>  	return flush;
>  }
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 7c5dd83e52de..9d03f5b127dc 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1034,8 +1034,8 @@ bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,
>  	struct kvm_mmu_page *root;
>  
>  	for_each_tdp_mmu_root(kvm, root, range->slot->as_id)

Another issue is that this should be for_each_tdp_mmu_root_yield_safe().  I'll get
a patch out for that later today.

> -		flush |= zap_gfn_range(kvm, root, range->start, range->end,
> -				       range->may_block, flush, false);
> +		flush = zap_gfn_range(kvm, root, range->start, range->end,
> +				      range->may_block, flush, false);
>  
>  	return flush;
>  }
> -- 
> 2.31.1
>