[PATCH v4 4/4] KVM: SVM: Add Bus Lock Detect support

[Ravi Bangoria <ravi.bangoria@xxxxxxx>]

Add Bus Lock Detect support in AMD SVM. Bus Lock Detect is enabled through
MSR_IA32_DEBUGCTLMSR and MSR_IA32_DEBUGCTLMSR is virtualized only if LBR
Virtualization is enabled. Add this dependency in the SVM.

Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
 arch/x86/kvm/svm/nested.c |  3 ++-
 arch/x86/kvm/svm/svm.c    | 17 ++++++++++++++---
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 6f704c1037e5..1df9158c72c1 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -586,7 +586,8 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 	/* These bits will be set properly on the first execution when new_vmc12 is true */
 	if (unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_DR))) {
 		vmcb02->save.dr7 = svm->nested.save.dr7 | DR7_FIXED_1;
-		svm->vcpu.arch.dr6  = svm->nested.save.dr6 | DR6_ACTIVE_LOW;
+		/* DR6_RTM is a reserved bit on AMD and as such must be set to 1 */
+		svm->vcpu.arch.dr6  = svm->nested.save.dr6 | DR6_FIXED_1 | DR6_RTM;
 		vmcb_mark_dirty(vmcb02, VMCB_DR);
 	}
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e1b6a16e97c0..9f3d31a5d231 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1047,7 +1047,8 @@ void svm_update_lbrv(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	bool current_enable_lbrv = svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK;
-	bool enable_lbrv = (svm_get_lbr_vmcb(svm)->save.dbgctl & DEBUGCTLMSR_LBR) ||
+	u64 dbgctl_buslock_lbr = DEBUGCTLMSR_BUS_LOCK_DETECT | DEBUGCTLMSR_LBR;
+	bool enable_lbrv = (svm_get_lbr_vmcb(svm)->save.dbgctl & dbgctl_buslock_lbr) ||
 			    (is_guest_mode(vcpu) && guest_can_use(vcpu, X86_FEATURE_LBRV) &&
 			    (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK));
 
@@ -3158,6 +3159,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		if (data & DEBUGCTL_RESERVED_BITS)
 			return 1;
 
+		if ((data & DEBUGCTLMSR_BUS_LOCK_DETECT) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
+			return 1;
+
 		svm_get_lbr_vmcb(svm)->save.dbgctl = data;
 		svm_update_lbrv(vcpu);
 		break;
@@ -5225,8 +5230,14 @@ static __init void svm_set_cpu_caps(void)
 	/* CPUID 0x8000001F (SME/SEV features) */
 	sev_set_cpu_caps();
 
-	/* Don't advertise Bus Lock Detect to guest if SVM support is absent */
-	kvm_cpu_cap_clear(X86_FEATURE_BUS_LOCK_DETECT);
+	/*
+	 * 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);
 }
 
 static __init int svm_hardware_setup(void)
-- 
2.34.1