linux-kernel - Re: [PATCH 1/3] KVM: x86/mmu: Drop a redundant, broken remote TLB flush

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Date:   Fri, 22 Oct 2021 18:39:29 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Maciej S . Szmigiero" <maciej.szmigiero@...cle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH 1/3] KVM: x86/mmu: Drop a redundant, broken remote TLB
 flush

On Thu, 2021-10-21 at 18:00 -0700, Sean Christopherson wrote:
> A recent commit to fix the calls to kvm_flush_remote_tlbs_with_address()
> in kvm_zap_gfn_range() inadvertantly added yet another flush instead of
> fixing the existing flush.  Drop the redundant flush, and fix the params
> for the existing flush.
> 
> Fixes: 2822da446640 ("KVM: x86/mmu: fix parameters to kvm_flush_remote_tlbs_with_address")
> Cc: Maxim Levitsky <mlevitsk@...hat.com>
> Cc: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index c6ddb042b281..f82b192bba0b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5709,13 +5709,11 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>  		for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
>  			flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, gfn_start,
>  							  gfn_end, flush);
> -		if (flush)
> -			kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
> -							   gfn_end - gfn_start);
>  	}
>  
>  	if (flush)
> -		kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);
> +		kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
> +						   gfn_end - gfn_start);
>  
>  	kvm_dec_notifier_count(kvm, gfn_start, gfn_end);
>  
Opps, I didn't notice that the revert added back another flush. I probablyhaven't had
the revert in place when I wrote the patch that fixed parameters to 
kvm_flush_remote_tlbs_with_address.

Best regards,
	Maxim Levitsky