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[v6,2/6] KVM: arm64: Add PSCI v1.3 SYSTEM_OFF2 function for hibernation

Message ID 20241019172459.2241939-3-dwmw2@infradead.org
State New
Headers show
Series Add PSCI v1.3 SYSTEM_OFF2 support for hibernation | expand

Commit Message

David Woodhouse Oct. 19, 2024, 5:15 p.m. UTC 
From: David Woodhouse <dwmw@amazon.co.uk>

The PSCI v1.3 specification adds support for a SYSTEM_OFF2 function
which is analogous to ACPI S4 state. This will allow hosting
environments to determine that a guest is hibernated rather than just
powered off, and ensure that they preserve the virtual environment
appropriately to allow the guest to resume safely (or bump the
hardware_signature in the FACS to trigger a clean reboot instead).

This feature is safe to enable unconditionally (in a subsequent commit)
because it is exposed to userspace through the existing
KVM_SYSTEM_EVENT_SHUTDOWN event, just with an additional flag which
userspace can use to know that the instance intended hibernation instead
of a plain power-off.

As with SYSTEM_RESET2, there is only one type available (in this case
HIBERNATE_OFF), and it is not explicitly reported to userspace through
the event; userspace can get it from the registers if it cares).

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 Documentation/virt/kvm/api.rst    | 11 ++++++++
 arch/arm64/include/uapi/asm/kvm.h |  6 +++++
 arch/arm64/kvm/psci.c             | 44 +++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+)
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index e32471977d0a..1ec076d806e6 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6855,6 +6855,10 @@  the first `ndata` items (possibly zero) of the data array are valid.
    the guest issued a SYSTEM_RESET2 call according to v1.1 of the PSCI
    specification.
 
+ - for arm64, data[0] is set to KVM_SYSTEM_EVENT_SHUTDOWN_FLAG_PSCI_OFF2
+   if the guest issued a SYSTEM_OFF2 call according to v1.3 of the PSCI
+   specification.
+
  - for RISC-V, data[0] is set to the value of the second argument of the
    ``sbi_system_reset`` call.
 
@@ -6888,6 +6892,13 @@  either:
  - Deny the guest request to suspend the VM. See ARM DEN0022D.b 5.19.2
    "Caller responsibilities" for possible return values.
 
+Hibernation using the PSCI SYSTEM_OFF2 call is enabled when PSCI v1.3
+is enabled. If a guest invokes the PSCI SYSTEM_OFF2 function, KVM will
+exit to userspace with the KVM_SYSTEM_EVENT_SHUTDOWN event type and with
+data[0] set to KVM_SYSTEM_EVENT_SHUTDOWN_FLAG_PSCI_OFF2. The only
+supported hibernate type for the SYSTEM_OFF2 function is HIBERNATE_OFF
+0x0).
+
 ::
 
 		/* KVM_EXIT_IOAPIC_EOI */
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 964df31da975..66736ff04011 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -484,6 +484,12 @@  enum {
  */
 #define KVM_SYSTEM_EVENT_RESET_FLAG_PSCI_RESET2	(1ULL << 0)
 
+/*
+ * Shutdown caused by a PSCI v1.3 SYSTEM_OFF2 call.
+ * Valid only when the system event has a type of KVM_SYSTEM_EVENT_SHUTDOWN.
+ */
+#define KVM_SYSTEM_EVENT_SHUTDOWN_FLAG_PSCI_OFF2	(1ULL << 0)
+
 /* run->fail_entry.hardware_entry_failure_reason codes. */
 #define KVM_EXIT_FAIL_ENTRY_CPU_UNSUPPORTED	(1ULL << 0)
 
diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
index 1f69b667332b..df834f2e928e 100644
--- a/arch/arm64/kvm/psci.c
+++ b/arch/arm64/kvm/psci.c
@@ -194,6 +194,12 @@  static void kvm_psci_system_off(struct kvm_vcpu *vcpu)
 	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_SHUTDOWN, 0);
 }
 
+static void kvm_psci_system_off2(struct kvm_vcpu *vcpu)
+{
+	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_SHUTDOWN,
+				 KVM_SYSTEM_EVENT_SHUTDOWN_FLAG_PSCI_OFF2);
+}
+
 static void kvm_psci_system_reset(struct kvm_vcpu *vcpu)
 {
 	kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_RESET, 0);
@@ -358,6 +364,11 @@  static int kvm_psci_1_x_call(struct kvm_vcpu *vcpu, u32 minor)
 			if (minor >= 1)
 				val = 0;
 			break;
+		case PSCI_1_3_FN_SYSTEM_OFF2:
+		case PSCI_1_3_FN64_SYSTEM_OFF2:
+			if (minor >= 3)
+				val = PSCI_1_3_OFF_TYPE_HIBERNATE_OFF;
+			break;
 		}
 		break;
 	case PSCI_1_0_FN_SYSTEM_SUSPEND:
@@ -392,6 +403,39 @@  static int kvm_psci_1_x_call(struct kvm_vcpu *vcpu, u32 minor)
 			break;
 		}
 		break;
+	case PSCI_1_3_FN_SYSTEM_OFF2:
+		kvm_psci_narrow_to_32bit(vcpu);
+		fallthrough;
+	case PSCI_1_3_FN64_SYSTEM_OFF2:
+		if (minor < 3)
+			break;
+
+		arg = smccc_get_arg1(vcpu);
+		/*
+		 * PSCI v1.3 issue F.b requires that zero be accepted to mean
+		 * HIBERNATE_OFF (in line with pre-publication versions of the
+		 * spec, and thus some actual implementations in the wild).
+		 * The second argument must be zero.
+		 */
+		if ((arg && arg != PSCI_1_3_OFF_TYPE_HIBERNATE_OFF) ||
+		    smccc_get_arg2(vcpu) != 0) {
+			val = PSCI_RET_INVALID_PARAMS;
+			break;
+		}
+		kvm_psci_system_off2(vcpu);
+		/*
+		 * We shouldn't be going back to guest VCPU after
+		 * receiving SYSTEM_OFF2 request.
+		 *
+		 * If user space accidentally/deliberately resumes
+		 * guest VCPU after SYSTEM_OFF2 request then guest
+		 * VCPU should see internal failure from PSCI return
+		 * value. To achieve this, we preload r0 (or x0) with
+		 * PSCI return value INTERNAL_FAILURE.
+		 */
+		val = PSCI_RET_INTERNAL_FAILURE;
+		ret = 0;
+		break;
 	default:
 		return kvm_psci_0_2_call(vcpu);
 	}