KVM: arm64: Indicate SYSTEM_RESET2 in kvm_run::system_event flags field

When handling reset and power-off PSCI calls from the guest, we
initialise X0 to PSCI_RET_INTERNAL_FAILURE in case the VMM tries to
re-run the vCPU after issuing the call.

Unfortunately, this also means that the VMM cannot see which PSCI call
was issued and therefore cannot distinguish between PSCI SYSTEM_RESET
and SYSTEM_RESET2 calls, which is necessary in order to determine the
validity of the "reset_type" in X1.

Allocate bit 0 of the previously unused 'flags' field of the
system_event structure so that we can indicate the PSCI call used to
initiate the reset.

Cc: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220221153524.15397-4-will@kernel.org

Documentation/virt/kvm/api.rst

@@ -5939,6 +5939,11 @@ Valid values for 'type' are:
    to ignore the request, or to gather VM memory core dump and/or
    reset/shutdown of the VM.
 
+Valid flags are:
+
+ - KVM_SYSTEM_EVENT_RESET_FLAG_PSCI_RESET2 (arm64 only) -- the guest issued
+   a SYSTEM_RESET2 call according to v1.1 of the PSCI specification.
+
 ::
 
 		/* KVM_EXIT_IOAPIC_EOI */

arch/arm64/include/uapi/asm/kvm.h

@@ -413,6 +413,13 @@ struct kvm_arm_copy_mte_tags {
 #define KVM_PSCI_RET_INVAL		PSCI_RET_INVALID_PARAMS
 #define KVM_PSCI_RET_DENIED		PSCI_RET_DENIED
 
+/* arm64-specific kvm_run::system_event flags */
+/*
+ * Reset caused by a PSCI v1.1 SYSTEM_RESET2 call.
+ * Valid only when the system event has a type of KVM_SYSTEM_EVENT_RESET.
+ */
+#define KVM_SYSTEM_EVENT_RESET_FLAG_PSCI_RESET2	(1ULL << 0)
+
 #endif
 
 #endif /* __ARM_KVM_H__ */

arch/arm64/kvm/psci.c

@@ -162,7 +162,7 @@ static unsigned long kvm_psci_vcpu_affinity_info(struct kvm_vcpu *vcpu)
 	return PSCI_0_2_AFFINITY_LEVEL_OFF;
 }
 
-static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type)
+static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type, u64 flags)
 {
 	unsigned long i;
 	struct kvm_vcpu *tmp;
@@ -182,17 +182,24 @@ static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type)
 
 	memset(&vcpu->run->system_event, 0, sizeof(vcpu->run->system_event));
 	vcpu->run->system_event.type = type;
+	vcpu->run->system_event.flags = flags;
 	vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
 }
 
 static void kvm_psci_system_off(struct kvm_vcpu *vcpu)
 {
-	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_SHUTDOWN);
+	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_SHUTDOWN, 0);
 }
 
 static void kvm_psci_system_reset(struct kvm_vcpu *vcpu)
 {
-	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_RESET);
+	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_RESET, 0);
+}
+
+static void kvm_psci_system_reset2(struct kvm_vcpu *vcpu)
+{
+	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_RESET,
+				 KVM_SYSTEM_EVENT_RESET_FLAG_PSCI_RESET2);
 }
 
 static void kvm_psci_narrow_to_32bit(struct kvm_vcpu *vcpu)
@@ -364,7 +371,7 @@ static int kvm_psci_1_x_call(struct kvm_vcpu *vcpu, u32 minor)
 			    arg < PSCI_1_1_RESET_TYPE_VENDOR_START) {
 				val = PSCI_RET_INVALID_PARAMS;
 			} else {
-				kvm_psci_system_reset(vcpu);
+				kvm_psci_system_reset2(vcpu);
 				val = PSCI_RET_INTERNAL_FAILURE;
 				ret = 0;
 			}