linux-kernel - [PATCH v2 23/23] kvm: x86: Disable RDMSR interception of IA32_XFD

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Date:   Fri, 17 Dec 2021 07:30:03 -0800
From:   Jing Liu <jing2.liu@...el.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        guang.zeng@...el.com, wei.w.wang@...el.com, yang.zhong@...el.com
Subject: [PATCH v2 23/23] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR

Also disable read emulation of IA32_XFD_ERR MSR at the same point
where r/w emulation of IA32_XFD MSR is disabled. 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.

Signed-off-by: Jing Liu <jing2.liu@...el.com>
---
 arch/x86/kvm/vmx/vmx.c | 2 ++
 arch/x86/kvm/vmx/vmx.h | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 97a823a3f23f..b66a005f076b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -163,6 +163,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
 	MSR_GS_BASE,
 	MSR_KERNEL_GS_BASE,
 	MSR_IA32_XFD,
+	MSR_IA32_XFD_ERR,
 #endif
 	MSR_IA32_SYSENTER_CS,
 	MSR_IA32_SYSENTER_ESP,
@@ -1934,6 +1935,7 @@ static u64 vcpu_supported_debugctl(struct kvm_vcpu *vcpu)
 static void vmx_set_xfd_passthrough(struct kvm_vcpu *vcpu)
 {
 	vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD, MSR_TYPE_RW);
+	vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R);
 	vcpu->arch.xfd_out_of_sync = true;
 }
 #endif
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index bf9d3051cd6c..0a00242a91e7 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	14
+#define MAX_POSSIBLE_PASSTHROUGH_MSRS	15
 	struct {
 		DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
 		DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);
-- 
2.27.0