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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id p32sm33734547pgb.49.2022.01.04.11.34.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Jan 2022 11:34:40 -0800 (PST) Date: Tue, 4 Jan 2022 19:34:36 +0000 From: Sean Christopherson To: Yang Zhong Cc: x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, pbonzini@redhat.com, corbet@lwn.net, shuah@kernel.org, jun.nakajima@intel.com, kevin.tian@intel.com, jing2.liu@linux.intel.com, jing2.liu@intel.com, guang.zeng@intel.com, wei.w.wang@intel.com Subject: Re: [PATCH v4 14/21] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR Message-ID: References: <20211229131328.12283-1-yang.zhong@intel.com> <20211229131328.12283-15-yang.zhong@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211229131328.12283-15-yang.zhong@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Dec 29, 2021, Yang Zhong wrote: > From: Jing Liu > > Disable read emulation of IA32_XFD_ERR MSR if guest cpuid includes XFD. > This saves one unnecessary VM-exit in guest #NM handler, given that the > MSR is already restored with the guest value before the guest is resumed. > > Suggested-by: Paolo Bonzini > Signed-off-by: Jing Liu > Signed-off-by: Yang Zhong > --- > arch/x86/kvm/vmx/vmx.c | 6 ++++++ > arch/x86/kvm/vmx/vmx.h | 2 +- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 4e51de876085..638665b3e241 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = { > MSR_FS_BASE, > MSR_GS_BASE, > MSR_KERNEL_GS_BASE, > + MSR_IA32_XFD_ERR, > #endif > MSR_IA32_SYSENTER_CS, > MSR_IA32_SYSENTER_ESP, > @@ -7228,6 +7229,11 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) > } > } > > + if (boot_cpu_has(X86_FEATURE_XFD)) This should be kvm_cpu_cap_has(), not boot_cpu_has(). If 32-bit kernels don't suppress XFD in boot_cpu_data, then using boot_cpus_has() is wrong. And even if XFD is suppressed, using kvm_cpu_cap_has() is still preferable. > + vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R, > + !guest_cpuid_has(vcpu, X86_FEATURE_XFD)); > + > + > set_cr4_guest_host_mask(vmx); > > vmx_write_encls_bitmap(vcpu, NULL); > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index 4df2ac24ffc1..bf9d3051cd6c 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -340,7 +340,7 @@ struct vcpu_vmx { > struct lbr_desc lbr_desc; > > /* Save desired MSR intercept (read: pass-through) state */ > -#define MAX_POSSIBLE_PASSTHROUGH_MSRS 13 > +#define MAX_POSSIBLE_PASSTHROUGH_MSRS 14 > struct { > DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS); > DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);