linux-kernel - Re: [PATCH 12/21] KVM: x86/mmu: Skip filling the gfn cache for guaranteed direct MMU topups

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Date:   Wed, 10 Jun 2020 11:52:35 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Marc Zyngier <maz@...nel.org>, Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Feiner <pfeiner@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [PATCH 12/21] KVM: x86/mmu: Skip filling the gfn cache for
 guaranteed direct MMU topups

On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Don't bother filling the gfn array cache when the caller is a fully
> direct MMU, i.e. won't need a gfn array for shadow pages.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Ben Gardon <bgardon@...gle.com>
> ---
>  arch/x86/kvm/mmu/mmu.c         | 18 ++++++++++--------
>  arch/x86/kvm/mmu/paging_tmpl.h |  4 ++--
>  2 files changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a8f8eebf67df..8d66cf558f1b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1101,7 +1101,7 @@ static void mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc)
>         }
>  }
>
> -static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu)
> +static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
>  {
>         int r;
>
> @@ -1114,10 +1114,12 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu)
>                                    PT64_ROOT_MAX_LEVEL);
>         if (r)
>                 return r;
> -       r = mmu_topup_memory_cache(&vcpu->arch.mmu_gfn_array_cache,
> -                                  PT64_ROOT_MAX_LEVEL);
> -       if (r)
> -               return r;
> +       if (maybe_indirect) {
> +               r = mmu_topup_memory_cache(&vcpu->arch.mmu_gfn_array_cache,
> +                                          PT64_ROOT_MAX_LEVEL);
> +               if (r)
> +                       return r;
> +       }
>         return mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache,
>                                       PT64_ROOT_MAX_LEVEL);
>  }
> @@ -4107,7 +4109,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>         if (fast_page_fault(vcpu, gpa, error_code))
>                 return RET_PF_RETRY;
>
> -       r = mmu_topup_memory_caches(vcpu);
> +       r = mmu_topup_memory_caches(vcpu, false);
>         if (r)
>                 return r;
>
> @@ -5147,7 +5149,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
>  {
>         int r;
>
> -       r = mmu_topup_memory_caches(vcpu);
> +       r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->direct_map);
>         if (r)
>                 goto out;
>         r = mmu_alloc_roots(vcpu);
> @@ -5341,7 +5343,7 @@ static void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>          * or not since pte prefetch is skiped if it does not have
>          * enough objects in the cache.
>          */
> -       mmu_topup_memory_caches(vcpu);
> +       mmu_topup_memory_caches(vcpu, true);
>
>         spin_lock(&vcpu->kvm->mmu_lock);
>
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 3de32122f601..ac39710d0594 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -818,7 +818,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
>                 return RET_PF_EMULATE;
>         }
>
> -       r = mmu_topup_memory_caches(vcpu);
> +       r = mmu_topup_memory_caches(vcpu, true);
>         if (r)
>                 return r;
>
> @@ -905,7 +905,7 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
>          * No need to check return value here, rmap_can_add() can
>          * help us to skip pte prefetch later.
>          */
> -       mmu_topup_memory_caches(vcpu);
> +       mmu_topup_memory_caches(vcpu, true);
>
>         if (!VALID_PAGE(root_hpa)) {
>                 WARN_ON(1);
> --
> 2.26.0
>