[PATCH v8 03/14] KVM/x86: KVM_CAP_X86_GUEST_LBR

[Wei Wang <wei.w.wang@xxxxxxxxx>]

Introduce KVM_CAP_X86_GUEST_LBR to allow per-VM enabling of the guest
lbr feature.

Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
---
 Documentation/virt/kvm/api.txt  | 26 ++++++++++++++++++++++++++
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/x86.c              | 16 ++++++++++++++++
 include/uapi/linux/kvm.h        |  1 +
 4 files changed, 45 insertions(+)

diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
index 2d06776..64632a8 100644
--- a/Documentation/virt/kvm/api.txt
+++ b/Documentation/virt/kvm/api.txt
@@ -5046,6 +5046,32 @@ it hard or impossible to use it correctly.  The availability of
 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 signals that those bugs are fixed.
 Userspace should not try to use KVM_CAP_MANUAL_DIRTY_LOG_PROTECT.
 
+7.19 KVM_CAP_X86_GUEST_LBR
+Architectures: x86
+Parameters: args[0] whether feature should be enabled or not
+            args[1] pointer to the userspace memory to load the lbr stack info
+
+The lbr stack info is described by
+struct x86_perf_lbr_stack {
+	unsigned int	nr;
+	unsigned int	tos;
+	unsigned int	from;
+	unsigned int	to;
+	unsigned int	info;
+};
+
+@nr: number of lbr stack entries
+@tos: index of the top of stack msr
+@from: index of the msr that stores a branch source address
+@to: index of the msr that stores a branch destination address
+@info: index of the msr that stores lbr related flags
+
+Enabling this capability allows guest accesses to the lbr feature. Otherwise,
+#GP will be injected to the guest when it accesses to the lbr related msrs.
+
+After the feature is enabled, before exiting to userspace, kvm handlers should
+fill the lbr stack info into the userspace memory pointed by args[1].
+
 8. Other capabilities.
 ----------------------
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7b0a4ee..d29dddd 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -875,6 +875,7 @@ struct kvm_arch {
 	atomic_t vapics_in_nmi_mode;
 	struct mutex apic_map_lock;
 	struct kvm_apic_map *apic_map;
+	struct x86_perf_lbr_stack lbr_stack;
 
 	bool apic_access_page_done;
 
@@ -884,6 +885,7 @@ struct kvm_arch {
 	bool hlt_in_guest;
 	bool pause_in_guest;
 	bool cstate_in_guest;
+	bool lbr_in_guest;
 
 	unsigned long irq_sources_bitmap;
 	s64 kvmclock_offset;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c6d951c..e1eb1be 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3129,6 +3129,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_EXCEPTION_PAYLOAD:
 		r = 1;
 		break;
+	case KVM_CAP_X86_GUEST_LBR:
+		r = sizeof(struct x86_perf_lbr_stack);
+		break;
 	case KVM_CAP_SYNC_REGS:
 		r = KVM_SYNC_X86_VALID_FIELDS;
 		break;
@@ -4670,6 +4673,19 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		kvm->arch.exception_payload_enabled = cap->args[0];
 		r = 0;
 		break;
+	case KVM_CAP_X86_GUEST_LBR:
+		r = -EINVAL;
+		if (cap->args[0] &&
+		    x86_perf_get_lbr_stack(&kvm->arch.lbr_stack))
+			break;
+
+		if (copy_to_user((void __user *)cap->args[1],
+				 &kvm->arch.lbr_stack,
+				 sizeof(struct x86_perf_lbr_stack)))
+			break;
+		kvm->arch.lbr_in_guest = cap->args[0];
+		r = 0;
+		break;
 	default:
 		r = -EINVAL;
 		break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5e3f12d..dd53edc 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -996,6 +996,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_ARM_PTRAUTH_ADDRESS 171
 #define KVM_CAP_ARM_PTRAUTH_GENERIC 172
 #define KVM_CAP_PMU_EVENT_FILTER 173
+#define KVM_CAP_X86_GUEST_LBR 174
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.7.4