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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id j10sm2133105wrx.30.2019.11.13.01.20.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Nov 2019 01:20:18 -0800 (PST) From: Vitaly Kuznetsov To: Liran Alon Cc: sean.j.christopherson@intel.com, jmattson@google.com, Liran Alon , Bhavesh Davda , pbonzini@redhat.com, rkrcmar@redhat.com, kvm@vger.kernel.org Subject: Re: [PATCH] KVM: x86: Optimization: Requst TLB flush in fast_cr3_switch() instead of do it directly In-Reply-To: <20191112183300.6959-1-liran.alon@oracle.com> References: <20191112183300.6959-1-liran.alon@oracle.com> Date: Wed, 13 Nov 2019 10:20:18 +0100 Message-ID: <87h838ku99.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 X-MC-Unique: UMacf3GDODCkCuq7_QBQ1A-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Liran Alon writes: > When KVM emulates a nested VMEntry (L1->L2 VMEntry), it switches mmu root > page. If nEPT is used, this will happen from > kvm_init_shadow_ept_mmu()->__kvm_mmu_new_cr3() and otherwise it will > happpen from nested_vmx_load_cr3()->kvm_mmu_new_cr3(). Either case, > __kvm_mmu_new_cr3() will use fast_cr3_switch() in attempt to switch to a > previously cached root page. > > In case fast_cr3_switch() finds a matching cached root page, it will > set it in mmu->root_hpa and request KVM_REQ_LOAD_CR3 such that on > next entry to guest, KVM will set root HPA in appropriate hardware > fields (e.g. vmcs->eptp). In addition, fast_cr3_switch() calls > kvm_x86_ops->tlb_flush() in order to flush TLB as MMU root page > was replaced. > > This works as mmu->root_hpa, which vmx_flush_tlb() use, was > already replaced in cached_root_available(). However, this may > result in unnecessary INVEPT execution because a KVM_REQ_TLB_FLUSH > may have already been requested. For example, by prepare_vmcs02() > in case L1 don't use VPID. > > Therefore, change fast_cr3_switch() to just request TLB flush on > next entry to guest. > > Reviewed-by: Bhavesh Davda > Signed-off-by: Liran Alon > --- > arch/x86/kvm/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 24c23c66b226..150d982ec1d2 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -4295,7 +4295,7 @@ static bool fast_cr3_switch(struct kvm_vcpu *vcpu, = gpa_t new_cr3, > =09=09=09kvm_make_request(KVM_REQ_LOAD_CR3, vcpu); > =09=09=09if (!skip_tlb_flush) { > =09=09=09=09kvm_make_request(KVM_REQ_MMU_SYNC, vcpu); > -=09=09=09=09kvm_x86_ops->tlb_flush(vcpu, true); > +=09=09=09=09kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu); > =09=09=09} > =20 > =09=09=09/* Reviewed-by: Vitaly Kuznetsov --=20 Vitaly