KVM: x86: nSVM: implement nested LBR virtualization

This was tested with kvm-unit-test that was developed
for this purpose.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220322174050.241850-3-mlevitsk@redhat.com>
[Copy all of DEBUGCTL except for reserved bits. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -588,8 +588,18 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 		vmcb_mark_dirty(vmcb02, VMCB_DR);
 	}
 
-	if (unlikely(vmcb01->control.virt_ext & LBR_CTL_ENABLE_MASK))
+	if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
+		/*
+		 * Reserved bits of DEBUGCTL are ignored.  Be consistent with
+		 * svm_set_msr's definition of reserved bits.
+		 */
+		svm_copy_lbrs(vmcb02, vmcb12);
+		vmcb02->save.dbgctl &= ~DEBUGCTL_RESERVED_BITS;
+		svm_update_lbrv(&svm->vcpu);
+
+	} else if (unlikely(vmcb01->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
 		svm_copy_lbrs(vmcb02, vmcb01);
+	}
 }
 
 static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
@@ -651,6 +661,9 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 
 	vmcb02->control.virt_ext            = vmcb01->control.virt_ext &
 					      LBR_CTL_ENABLE_MASK;
+	if (svm->lbrv_enabled)
+		vmcb02->control.virt_ext  |=
+			(svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK);
 
 	if (!nested_vmcb_needs_vls_intercept(svm))
 		vmcb02->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
@@ -919,7 +932,10 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	svm_switch_vmcb(svm, &svm->vmcb01);
 
-	if (unlikely(vmcb01->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
+	if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
+		svm_copy_lbrs(vmcb12, vmcb02);
+		svm_update_lbrv(vcpu);
+	} else if (unlikely(vmcb01->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
 		svm_copy_lbrs(vmcb01, vmcb02);
 		svm_update_lbrv(vcpu);
 	}

arch/x86/kvm/svm/svm.c

@@ -62,8 +62,6 @@ MODULE_DEVICE_TABLE(x86cpu, svm_cpu_id);
 #define SEG_TYPE_LDT 2
 #define SEG_TYPE_BUSY_TSS16 3
 
-#define DEBUGCTL_RESERVED_BITS (~(0x3fULL))
-
 static bool erratum_383_found __read_mostly;
 
 u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
@@ -878,6 +876,10 @@ void svm_update_lbrv(struct kvm_vcpu *vcpu)
 	bool current_enable_lbrv = !!(svm->vmcb->control.virt_ext &
 				      LBR_CTL_ENABLE_MASK);
 
+	if (unlikely(is_guest_mode(vcpu) && svm->lbrv_enabled))
+		if (unlikely(svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))
+			enable_lbrv = true;
+
 	if (enable_lbrv == current_enable_lbrv)
 		return;
 
@@ -4012,6 +4014,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 			     guest_cpuid_has(vcpu, X86_FEATURE_NRIPS);
 
 	svm->tsc_scaling_enabled = tsc_scaling && guest_cpuid_has(vcpu, X86_FEATURE_TSCRATEMSR);
+	svm->lbrv_enabled = lbrv && guest_cpuid_has(vcpu, X86_FEATURE_LBRV);
 
 	svm->v_vmload_vmsave_enabled = vls && guest_cpuid_has(vcpu, X86_FEATURE_V_VMSAVE_VMLOAD);
 
@@ -4765,6 +4768,8 @@ static __init void svm_set_cpu_caps(void)
 
 		if (vls)
 			kvm_cpu_cap_set(X86_FEATURE_V_VMSAVE_VMLOAD);
+		if (lbrv)
+			kvm_cpu_cap_set(X86_FEATURE_LBRV);
 
 		/* Nested VM can receive #VMEXIT instead of triggering #GP */
 		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);

arch/x86/kvm/svm/svm.h

@@ -236,6 +236,7 @@ struct vcpu_svm {
 	bool nrips_enabled                : 1;
 	bool tsc_scaling_enabled          : 1;
 	bool v_vmload_vmsave_enabled      : 1;
+	bool lbrv_enabled                 : 1;
 
 	u32 ldr_reg;
 	u32 dfr_reg;
@@ -486,6 +487,8 @@ static inline bool nested_npt_enabled(struct vcpu_svm *svm)
 /* svm.c */
 #define MSR_INVALID				0xffffffffU
 
+#define DEBUGCTL_RESERVED_BITS (~(0x3fULL))
+
 extern bool dump_invalid_vmcb;
 
 u32 svm_msrpm_offset(u32 msr);