From:   Jing Liu <jing2.liu@intel.com>
To:     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
Cc:     seanjc@google.com, 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, yang.zhong@intel.com
Subject: [PATCH v3 15/22] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR
Date:   Wed, 22 Dec 2021 04:40:45 -0800
Message-Id: <20211222124052.644626-16-jing2.liu@intel.com>
In-Reply-To: <20211222124052.644626-1-jing2.liu@intel.com>
References: <20211222124052.644626-1-jing2.liu@intel.com>
MIME-Version: 1.0
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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 <pbonzini@redhat.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
---
 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 57d256fbf34b..8595a3e8fbd8 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,
@@ -7225,6 +7226,11 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		}
 	}
 
+	if (boot_cpu_has(X86_FEATURE_XFD))
+		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);
-- 
2.27.0