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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id e18-20020a056a001a9200b004bc82d0e125sm20015997pfv.119.2022.03.08.08.16.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Mar 2022 08:16:34 -0800 (PST) Date: Tue, 8 Mar 2022 16:16:31 +0000 From: Sean Christopherson To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, dmatlack@google.com Subject: Re: [PATCH v2 01/25] KVM: x86/mmu: avoid indirect call for get_cr3 Message-ID: References: <20220221162243.683208-1-pbonzini@redhat.com> <20220221162243.683208-2-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220221162243.683208-2-pbonzini@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 21, 2022, Paolo Bonzini wrote: > Most of the time, calls to get_guest_pgd result in calling kvm_read_cr3 > (the exception is only nested TDP). Check if that is the case if > retpolines are enabled, thus avoiding an expensive indirect call. > > Signed-off-by: Paolo Bonzini > --- > arch/x86/kvm/mmu.h | 10 ++++++++++ > arch/x86/kvm/mmu/mmu.c | 15 ++++++++------- > arch/x86/kvm/mmu/paging_tmpl.h | 2 +- > arch/x86/kvm/x86.c | 2 +- > 4 files changed, 20 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index 1d0c1904d69a..6ee4436e46f1 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -116,6 +116,16 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu) > vcpu->arch.mmu->shadow_root_level); > } > > +extern unsigned long kvm_get_guest_cr3(struct kvm_vcpu *vcpu); No extern please, it's superfluous and against KVM style. Moot point though, see below. > +static inline unsigned long kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) Wrap the params, no reason to make this line so long. > +{ > +#ifdef CONFIG_RETPOLINE > + if (mmu->get_guest_pgd == kvm_get_guest_cr3) > + return kvm_read_cr3(vcpu); This is unnecessarily fragile and confusing at first glance. Compilers are smart enough to generate a non-inline version of functions if they're used for function pointers, while still inlining where appropriate. In other words, just drop kvm_get_guest_cr3() entirely, a al get_pdptr => kvm_pdptr_read(). --- arch/x86/kvm/mmu.h | 6 +++--- arch/x86/kvm/mmu/mmu.c | 11 +++-------- 2 files changed, 6 insertions(+), 11 deletions(-) diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 3af66b9df640..50528d39de8d 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -117,11 +117,11 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu) vcpu->arch.mmu->shadow_root_level); } -extern unsigned long kvm_get_guest_cr3(struct kvm_vcpu *vcpu); -static inline unsigned long kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) +static inline unsigned long kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu, + struct kvm_mmu *mmu) { #ifdef CONFIG_RETPOLINE - if (mmu->get_guest_pgd == kvm_get_guest_cr3) + if (mmu->get_guest_pgd == kvm_read_cr3) return kvm_read_cr3(vcpu); #endif return mmu->get_guest_pgd(vcpu); diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 995c3450c20f..cc2414397e4b 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4234,11 +4234,6 @@ void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd) } EXPORT_SYMBOL_GPL(kvm_mmu_new_pgd); -unsigned long kvm_get_guest_cr3(struct kvm_vcpu *vcpu) -{ - return kvm_read_cr3(vcpu); -} - static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn, unsigned int access) { @@ -4793,7 +4788,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu) context->invlpg = NULL; context->shadow_root_level = kvm_mmu_get_tdp_level(vcpu); context->direct_map = true; - context->get_guest_pgd = kvm_get_guest_cr3; + context->get_guest_pgd = kvm_read_cr3; context->get_pdptr = kvm_pdptr_read; context->inject_page_fault = kvm_inject_page_fault; context->root_level = role_regs_to_root_level(®s); @@ -4968,7 +4963,7 @@ static void init_kvm_softmmu(struct kvm_vcpu *vcpu) kvm_init_shadow_mmu(vcpu, ®s); - context->get_guest_pgd = kvm_get_guest_cr3; + context->get_guest_pgd = kvm_read_cr3; context->get_pdptr = kvm_pdptr_read; context->inject_page_fault = kvm_inject_page_fault; } @@ -5000,7 +4995,7 @@ static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu) return; g_context->mmu_role.as_u64 = new_role.as_u64; - g_context->get_guest_pgd = kvm_get_guest_cr3; + g_context->get_guest_pgd = kvm_read_cr3; g_context->get_pdptr = kvm_pdptr_read; g_context->inject_page_fault = kvm_inject_page_fault; g_context->root_level = new_role.base.level; base-commit: c31df3e63672c14d8b52e34606c823e2166024b8 --