linux-kernel - [PATCH 17/19] KVM: VMX: Pass through CET MSRs to the guest when supported

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Date:   Thu, 16 Jun 2022 04:46:41 -0400
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     pbonzini@...hat.com, seanjc@...gle.com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rick.p.edgecombe@...el.com
Cc:     weijiang.yang@...el.com, Zhang Yi Z <yi.z.zhang@...ux.intel.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [PATCH 17/19] KVM: VMX: Pass through CET MSRs to the guest when supported

Pass through CET user mode MSRs when the associated CET component
is enabled to improve guest performance.  All CET MSRs are context
switched, either via dedicated VMCS fields or XSAVES.

Co-developed-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
---
 arch/x86/kvm/vmx/vmx.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4bdede87669a..9aebd67ff03e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -583,6 +583,9 @@ static bool is_valid_passthrough_msr(u32 msr)
 	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 8:
 		/* LBR MSRs. These are handled in vmx_update_intercept_for_lbr_msrs() */
 		return true;
+	case MSR_IA32_U_CET:
+	case MSR_IA32_PL3_SSP:
+		return true;
 	}
 
 	r = possible_passthrough_msr_slot(msr) != -ENOENT;
@@ -7595,6 +7598,23 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
 		vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
 }
 
+static bool is_cet_state_supported(struct kvm_vcpu *vcpu, u32 xss_state)
+{
+	return (kvm_caps.supported_xss & xss_state) &&
+	       (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+		guest_cpuid_has(vcpu, X86_FEATURE_IBT));
+}
+
+static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
+{
+	bool incpt = !is_cet_state_supported(vcpu, XFEATURE_MASK_CET_USER);
+
+	vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, incpt);
+
+	incpt |= !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
+	vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, incpt);
+}
+
 static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -7657,6 +7677,9 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
 	/* Refresh #PF interception to account for MAXPHYADDR changes. */
 	vmx_update_exception_bitmap(vcpu);
+
+	if (kvm_cet_user_supported())
+		vmx_update_intercept_for_cet_msr(vcpu);
 }
 
 static __init void vmx_set_cpu_caps(void)
-- 
2.27.0