[PATCH v10 12/28] KVM: x86: Add a new save/restore flag for FRED metadata

[Sohil Mehta <sohil.mehta@intel.com>]

From: Xin Li <xin@zytor.com>

Introduce a new save/restore flag for FRED metadata (specifically, the
event nested flag and data) being saved and restored during VM save/
restore and live migration.

Signed-off-by: Xin Li <xin@zytor.com>
Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
---
v10:
 - Advertise KVM_CAP_X86_FRED_EVENT only when KVM can virtualize FRED, and
   return -EINVAL from KVM_ENABLE_CAP otherwise.
 - Document the new return value in api.rst.
---
 Documentation/virt/kvm/api.rst  | 22 ++++++++++++++++++++++
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/include/uapi/asm/kvm.h |  1 +
 arch/x86/kvm/x86.c              | 18 ++++++++++++++++++
 include/uapi/linux/kvm.h        |  1 +
 5 files changed, 43 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 4eb7e75a7473..22ef94f3eb3a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1199,6 +1199,10 @@ The following bits are defined in the flags field:
   triple_fault_pending field contains a valid state. This bit will
   be set whenever KVM_CAP_X86_TRIPLE_FAULT_EVENT is enabled.
 
+- KVM_VCPUEVENT_VALID_FRED_STATE may be set to inform that the exception
+  state includes FRED state (specifically, the event nested flag and data).
+  This bit will be set whenever KVM_CAP_X86_FRED_EVENT is enabled.
+
 ARM64:
 ^^^^^^
 
@@ -1301,6 +1305,11 @@ If KVM_CAP_X86_TRIPLE_FAULT_EVENT is enabled, KVM_VCPUEVENT_VALID_TRIPLE_FAULT
 can be set in flags field to signal that the triple_fault field contains
 a valid state and shall be written into the VCPU.
 
+If KVM_CAP_X86_FRED_EVENT is enabled, KVM_VCPUEVENT_VALID_FRED_STATE can be set
+in the flags field to inform that the exception state contains FRED state
+(specifically, the event nested flag and data), which shall be written into the
+VCPU.
+
 ARM64:
 ^^^^^^
 
@@ -8979,6 +8988,19 @@ enabled, cmma can't be enabled anymore and pfmfi and the storage key
 interpretation are disabled. If cmma has already been enabled or the
 hpage_2g module parameter is not set to 1, -EINVAL is returned.
 
+7.48 KVM_CAP_X86_FRED_EVENT
+---------------------------
+
+:Architectures: x86
+:Parameters: args[0] whether feature should be enabled or not
+:Returns: 0 on success; -EINVAL if KVM cannot virtualize FRED.
+
+With this capability enabled, KVM allows exception save and restore operations
+to include FRED event context (specifically, the event nested flag and data).
+When injecting a FRED exception during VM entry, FRED event delivery relies
+on this information to select the correct event stack level and apply proper
+event data.
+
 8. Other capabilities.
 ======================
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0fd5d4edeebb..dd68db17fdae 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1286,6 +1286,7 @@ struct kvm_arch {
 	bool has_mapped_host_mmio;
 	bool guest_can_read_msr_platform_info;
 	bool exception_payload_enabled;
+	bool exception_fred_state_enabled;
 
 	bool triple_fault_event;
 
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 1585ec804066..6a67832c59bb 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -331,6 +331,7 @@ struct kvm_reinject_control {
 #define KVM_VCPUEVENT_VALID_SMM		0x00000008
 #define KVM_VCPUEVENT_VALID_PAYLOAD	0x00000010
 #define KVM_VCPUEVENT_VALID_TRIPLE_FAULT	0x00000020
+#define KVM_VCPUEVENT_VALID_FRED_STATE	0x00000040
 
 /* Interrupt shadow states */
 #define KVM_X86_SHADOW_INT_MOV_SS	0x01
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4b3681796c75..01198aba27cf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2288,6 +2288,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_PRE_FAULT_MEMORY:
 		r = tdp_enabled;
 		break;
+	case KVM_CAP_X86_FRED_EVENT:
+		r = kvm_cpu_cap_has(X86_FEATURE_FRED);
+		break;
 	case KVM_CAP_X86_APIC_BUS_CYCLES_NS:
 		r = kvm ? kvm->arch.apic_bus_cycle_ns : APIC_BUS_CYCLE_NS_DEFAULT;
 		break;
@@ -3022,6 +3025,8 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
 			 | KVM_VCPUEVENT_VALID_SMM);
 	if (vcpu->kvm->arch.exception_payload_enabled)
 		events->flags |= KVM_VCPUEVENT_VALID_PAYLOAD;
+	if (vcpu->kvm->arch.exception_fred_state_enabled)
+		events->flags |= KVM_VCPUEVENT_VALID_FRED_STATE;
 	if (vcpu->kvm->arch.triple_fault_event) {
 		events->triple_fault.pending = kvm_test_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 		events->flags |= KVM_VCPUEVENT_VALID_TRIPLE_FAULT;
@@ -3036,6 +3041,7 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 			      | KVM_VCPUEVENT_VALID_SHADOW
 			      | KVM_VCPUEVENT_VALID_SMM
 			      | KVM_VCPUEVENT_VALID_PAYLOAD
+			      | KVM_VCPUEVENT_VALID_FRED_STATE
 			      | KVM_VCPUEVENT_VALID_TRIPLE_FAULT))
 		return -EINVAL;
 
@@ -3051,6 +3057,11 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 		events->exception_has_payload = 0;
 	}
 
+	if (events->flags & KVM_VCPUEVENT_VALID_FRED_STATE) {
+		if (!vcpu->kvm->arch.exception_fred_state_enabled)
+			return -EINVAL;
+	}
+
 	if ((events->exception.injected || events->exception.pending) &&
 	    (events->exception.nr > 31 || events->exception.nr == NMI_VECTOR))
 		return -EINVAL;
@@ -4038,6 +4049,13 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		kvm->arch.exception_payload_enabled = cap->args[0];
 		r = 0;
 		break;
+	case KVM_CAP_X86_FRED_EVENT:
+		r = -EINVAL;
+		if (!kvm_cpu_cap_has(X86_FEATURE_FRED))
+			break;
+		kvm->arch.exception_fred_state_enabled = cap->args[0];
+		r = 0;
+		break;
 	case KVM_CAP_X86_TRIPLE_FAULT_EVENT:
 		kvm->arch.triple_fault_event = cap->args[0];
 		r = 0;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 9fc8dfdfd65f..c5ffc4e7ddb1 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -998,6 +998,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_S390_VSIE_ESAMODE 248
 #define KVM_CAP_S390_HPAGE_2G 249
 #define KVM_CAP_ARM_PMU_V3_STRICT 250
+#define KVM_CAP_X86_FRED_EVENT 251
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
-- 
2.43.0