[PATCH v6 12/12] KVM: SVM: Add support for virtualizating Bus Lock Detect

[Sean Christopherson <seanjc@google.com>]

From: Ravi Bangoria <ravi.bangoria@amd.com>

Advertise support for virtualizing Bus Lock Detect and allow the guest to
enable BUS_LOCK_DETECT if LBR Virtualization is enabled (Bus Lock Detect is
enabled through MSR_IA32_DEBUGCTLMSR, which context-switched if and only if
LBR Virtualization is enabled).

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Co-developed-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/svm.c | 12 ++++++++++--
 arch/x86/kvm/svm/svm.h |  7 ++++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1e58ad8691e9..e7c296c52591 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -879,7 +879,7 @@ static bool svm_need_lbr_virtualization(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	if (svm->vmcb->save.dbgctl & DEBUGCTLMSR_LBR)
+	if (svm->vmcb->save.dbgctl & (DEBUGCTLMSR_LBR | DEBUGCTLMSR_BUS_LOCK_DETECT))
 		return true;
 
 	return is_guest_mode(vcpu) &&
@@ -5712,9 +5712,17 @@ static __init void svm_set_cpu_caps(void)
 	 * Clear capabilities that are automatically configured by common code,
 	 * but that require explicit SVM support (that isn't yet implemented).
 	 */
-	kvm_cpu_cap_clear(X86_FEATURE_BUS_LOCK_DETECT);
 	kvm_cpu_cap_clear(X86_FEATURE_MSR_IMM);
 
+	/*
+	 * LBR Virtualization must be enabled to support BusLockTrap inside the
+	 * guest, since BusLockTrap is enabled through MSR_IA32_DEBUGCTLMSR and
+	 * MSR_IA32_DEBUGCTLMSR is virtualized only if LBR Virtualization is
+	 * enabled.
+	 */
+	if (!lbrv)
+		kvm_cpu_cap_clear(X86_FEATURE_BUS_LOCK_DETECT);
+
 	kvm_setup_xss_caps();
 	kvm_finalize_cpu_caps();
 }
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index c3380d865b75..6d0242966dc8 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -789,7 +789,12 @@ BUILD_SVM_MSR_BITMAP_HELPERS(void, set, __set)
 
 static inline u64 svm_get_supported_debugctl(struct kvm_vcpu *vcpu)
 {
-	return DEBUGCTLMSR_LBR;
+	u64 debugctl = DEBUGCTLMSR_LBR;
+
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
+		debugctl |= DEBUGCTLMSR_BUS_LOCK_DETECT;
+
+	return debugctl;
 }
 
 /* svm.c */
-- 
2.56.0.rc1.315.gc6ed9934b7-goog