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Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Tue,  4 May 2021 10:17:26 -0700
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Subject: [PATCH 07/15] KVM: x86: Add support for RDPID without RDTSCP
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xiaoyao Li <xiaoyao.li@intel.com>,
        Reiji Watanabe <reijiw@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Allow userspace to enable RDPID for a guest without also enabling RDTSCP.
Aside from checking for RDPID support in the obvious flows, VMX also needs
to set ENABLE_RDTSCP=1 when RDPID is exposed.

For the record, there is no known scenario where enabling RDPID without
RDTSCP is desirable.  But, both AMD and Intel architectures allow for the
condition, i.e. this is purely to make KVM more architecturally accurate.

Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
Cc: stable@vger.kernel.org
Reported-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/svm.c |  6 ++++--
 arch/x86/kvm/vmx/vmx.c | 27 +++++++++++++++++++++++----
 arch/x86/kvm/x86.c     |  3 ++-
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b3153d40cc4d..231b9650d864 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2669,7 +2669,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (tsc_aux_uret_slot < 0)
 			return 1;
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
 			return 1;
 		msr_info->data = svm->tsc_aux;
 		break;
@@ -2891,7 +2892,8 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 			return 1;
 
 		if (!msr->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
 			return 1;
 
 		/*
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 990ee339a05f..42e4bbaa299a 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1788,7 +1788,8 @@ static void setup_msrs(struct vcpu_vmx *vmx)
 	if (update_transition_efer(vmx))
 		vmx_setup_uret_msr(vmx, MSR_EFER);
 
-	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP))
+	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP)  ||
+	    guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID))
 		vmx_setup_uret_msr(vmx, MSR_TSC_AUX);
 
 	vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL);
@@ -1994,7 +1995,8 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_TSC_AUX:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
 			return 1;
 		goto find_uret_msr;
 	case MSR_IA32_DEBUGCTLMSR:
@@ -2314,7 +2316,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_TSC_AUX:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_RDPID))
 			return 1;
 		/* Check reserved bit, higher 32 bits should be zero */
 		if ((data >> 32) != 0)
@@ -4368,7 +4371,23 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
 						  xsaves_enabled, false);
 	}
 
-	vmx_adjust_sec_exec_feature(vmx, &exec_control, rdtscp, RDTSCP);
+	/*
+	 * RDPID is also gated by ENABLE_RDTSCP, turn on the control if either
+	 * feature is exposed to the guest.  This creates a virtualization hole
+	 * if both are supported in hardware but only one is exposed to the
+	 * guest, but letting the guest execute RDTSCP or RDPID when either one
+	 * is advertised is preferable to emulating the advertised instruction
+	 * in KVM on #UD, and obviously better than incorrectly injecting #UD.
+	 */
+	if (cpu_has_vmx_rdtscp()) {
+		bool rdpid_or_rdtscp_enabled =
+			guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP) ||
+			guest_cpuid_has(vcpu, X86_FEATURE_RDPID);
+
+		vmx_adjust_secondary_exec_control(vmx, &exec_control,
+						  SECONDARY_EXEC_ENABLE_RDTSCP,
+						  rdpid_or_rdtscp_enabled, false);
+	}
 	vmx_adjust_sec_exec_feature(vmx, &exec_control, invpcid, INVPCID);
 
 	vmx_adjust_sec_exec_exiting(vmx, &exec_control, rdrand, RDRAND);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e304447be42d..b4516d303413 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5978,7 +5978,8 @@ static void kvm_init_msr_list(void)
 				continue;
 			break;
 		case MSR_TSC_AUX:
-			if (!kvm_cpu_cap_has(X86_FEATURE_RDTSCP))
+			if (!kvm_cpu_cap_has(X86_FEATURE_RDTSCP) &&
+			    !kvm_cpu_cap_has(X86_FEATURE_RDPID))
 				continue;
 			break;
 		case MSR_IA32_UMWAIT_CONTROL:
-- 
2.31.1.527.g47e6f16901-goog