linux-kernel - Re: [PATCH v2 2/3] KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping

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Date:   Thu, 25 Mar 2021 14:47:53 -0700
From:   Ben Gardon <bgardon@...gle.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 <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU
 during NX zapping

On Thu, Mar 25, 2021 at 1:01 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Honor the "flush needed" return from kvm_tdp_mmu_zap_gfn_range(), which
> does the flush itself if and only if it yields (which it will never do in
> this particular scenario), and otherwise expects the caller to do the
> flush.  If pages are zapped from the TDP MMU but not the legacy MMU, then
> no flush will occur.
>
> Fixes: 29cf0f5007a2 ("kvm: x86/mmu: NX largepage recovery for TDP MMU")
> Cc: stable@...r.kernel.org
> Cc: Ben Gardon <bgardon@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Ben Gardon <bgardon@...gle.com>

> ---
>  arch/x86/kvm/mmu/mmu.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index c6ed633594a2..5a53743b37bc 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5939,6 +5939,8 @@ static void kvm_recover_nx_lpages(struct kvm *kvm)
>         struct kvm_mmu_page *sp;
>         unsigned int ratio;
>         LIST_HEAD(invalid_list);
> +       bool flush = false;
> +       gfn_t gfn_end;
>         ulong to_zap;
>
>         rcu_idx = srcu_read_lock(&kvm->srcu);
> @@ -5960,19 +5962,20 @@ static void kvm_recover_nx_lpages(struct kvm *kvm)
>                                       lpage_disallowed_link);
>                 WARN_ON_ONCE(!sp->lpage_disallowed);
>                 if (is_tdp_mmu_page(sp)) {
> -                       kvm_tdp_mmu_zap_gfn_range(kvm, sp->gfn,
> -                               sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level));
> +                       gfn_end = sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level);
> +                       flush = kvm_tdp_mmu_zap_gfn_range(kvm, sp->gfn, gfn_end);
>                 } else {
>                         kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
>                         WARN_ON_ONCE(sp->lpage_disallowed);
>                 }
>
>                 if (need_resched() || rwlock_needbreak(&kvm->mmu_lock)) {
> -                       kvm_mmu_commit_zap_page(kvm, &invalid_list);
> +                       kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, flush);
>                         cond_resched_rwlock_write(&kvm->mmu_lock);
> +                       flush = false;
>                 }
>         }
> -       kvm_mmu_commit_zap_page(kvm, &invalid_list);
> +       kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, flush);
>
>         write_unlock(&kvm->mmu_lock);
>         srcu_read_unlock(&kvm->srcu, rcu_idx);
> --
> 2.31.0.291.g576ba9dcdaf-goog
>