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

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Message-ID: <CAJhGHyCA-nfoJPmQxVWRtu+iJk3aj9ZdNH630RjrQJ_vYnZ3Gg@mail.gmail.com>
Date:   Fri, 22 Oct 2021 10:58:15 +0800
From:   Lai Jiangshan <jiangshanlai+lkml@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     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>, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        "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 Fri, Oct 22, 2021 at 9:01 AM Sean Christopherson <seanjc@...gle.com> 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);

In the recent queue branch of kvm tree, there is the same "if (flush)" in
the previous "if (kvm_memslots_have_rmaps(kvm))" branch.  The "if (flush)"
branch needs to be removed too.

Reviewed-by: Lai Jiangshan <jiangshanlai@...il.com>

>         }
>
>         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);
>
> --
> 2.33.0.1079.g6e70778dc9-goog
>