linux-kernel - Re: [PATCH v3 1/2] KVM: x86/mmu: Move flush logic from mmu_page_zap

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Date:   Wed, 23 Sep 2020 16:19:15 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.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,
        linux-kernel@...r.kernel.org, Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH v3 1/2] KVM: x86/mmu: Move flush logic from
 mmu_page_zap_pte() to FNAME(invlpg)

On Wed, Sep 23, 2020 at 3:14 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Move the logic that controls whether or not FNAME(invlpg) needs to flush
> fully into FNAME(invlpg) so that mmu_page_zap_pte() doesn't return a
> value.  This allows a future patch to redefine the return semantics for
> mmu_page_zap_pte() so that it can recursively zap orphaned child shadow
> pages for nested TDP MMUs.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>

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

>
> ---
>  arch/x86/kvm/mmu/mmu.c         | 10 +++-------
>  arch/x86/kvm/mmu/paging_tmpl.h |  7 +++++--
>  2 files changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 76c5826e29a2..a91e8601594d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2615,7 +2615,7 @@ static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>         }
>  }
>
> -static bool mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
> +static void mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
>                              u64 *spte)
>  {
>         u64 pte;
> @@ -2631,13 +2631,9 @@ static bool mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
>                         child = to_shadow_page(pte & PT64_BASE_ADDR_MASK);
>                         drop_parent_pte(child, spte);
>                 }
> -               return true;
> -       }
> -
> -       if (is_mmio_spte(pte))
> +       } else if (is_mmio_spte(pte)) {
>                 mmu_spte_clear_no_track(spte);
> -
> -       return false;
> +       }
>  }
>
>  static void kvm_mmu_page_unlink_children(struct kvm *kvm,
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 4dd6b1e5b8cf..3bb624a3dda9 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -895,6 +895,7 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
>  {
>         struct kvm_shadow_walk_iterator iterator;
>         struct kvm_mmu_page *sp;
> +       u64 old_spte;
>         int level;
>         u64 *sptep;
>
> @@ -917,7 +918,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
>                 sptep = iterator.sptep;
>
>                 sp = sptep_to_sp(sptep);
> -               if (is_last_spte(*sptep, level)) {
> +               old_spte = *sptep;
> +               if (is_last_spte(old_spte, level)) {
>                         pt_element_t gpte;
>                         gpa_t pte_gpa;
>
> @@ -927,7 +929,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
>                         pte_gpa = FNAME(get_level1_sp_gpa)(sp);
>                         pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);
>
> -                       if (mmu_page_zap_pte(vcpu->kvm, sp, sptep))
> +                       mmu_page_zap_pte(vcpu->kvm, sp, sptep);
> +                       if (is_shadow_present_pte(old_spte))
>                                 kvm_flush_remote_tlbs_with_address(vcpu->kvm,
>                                         sp->gfn, KVM_PAGES_PER_HPAGE(sp->role.level));
>
> --
> 2.28.0
>