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References: <20200605213853.14959-1-sean.j.christopherson@intel.com> <20200605213853.14959-7-sean.j.christopherson@intel.com>
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From:   Ben Gardon <bgardon@google.com>
Date:   Tue, 9 Jun 2020 16:03:40 -0700
Message-ID: <CANgfPd9Y9P+-got9HmtrvChmwZBe-XOA0zSSLMsPCUKcuBv4aQ@mail.gmail.com>
Subject: Re: [PATCH 06/21] KVM: x86/mmu: Move fast_page_fault() call above mmu_topup_memory_caches()
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Marc Zyngier <maz@kernel.org>, Paul Mackerras <paulus@ozlabs.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        David Hildenbrand <david@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-mips@vger.kernel.org, kvm@vger.kernel.org,
        kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Peter Feiner <pfeiner@google.com>,
        Peter Shier <pshier@google.com>,
        Junaid Shahid <junaids@google.com>,
        Christoffer Dall <christoffer.dall@arm.com>
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On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> Avoid refilling the memory caches and potentially slow reclaim/swap when
> handling a fast page fault, which does not need to allocate any new
> objects.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 5e773564ab20..4b4c3234d623 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4095,6 +4095,9 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>         if (page_fault_handle_page_track(vcpu, error_code, gfn))
>                 return RET_PF_EMULATE;
>
> +       if (fast_page_fault(vcpu, gpa, error_code))
> +               return RET_PF_RETRY;
> +
>         r = mmu_topup_memory_caches(vcpu);
>         if (r)
>                 return r;
> @@ -4102,9 +4105,6 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>         if (lpage_disallowed)
>                 max_level = PG_LEVEL_4K;
>
> -       if (fast_page_fault(vcpu, gpa, error_code))
> -               return RET_PF_RETRY;
> -
>         mmu_seq = vcpu->kvm->mmu_notifier_seq;
>         smp_rmb();
>
> --
> 2.26.0
>