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 11:03:15 +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 10:58 AM Lai Jiangshan
<jiangshanlai+lkml@...il.com> wrote:
>
> 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.

Oh, it is in the patch 2. For patch 1 and 2:

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

>
> 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
> >