[PATCH v5 2/5] KVM: arm64: Add PSCI v1.3 SYSTEM_OFF2 function for hibernation

David Woodhouse
2024-09-26T18:46:07Z

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).

Although this new feature is inflicted unconditionally on unexpecting
userspace, it should be OK because it still results in the same
KVM_SYSTEM_EVENT_SHUTDOWN event, just with a new flag which hopefully
won't cause userspace to get unhappy.

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 | 37 +++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index b3be87489108..2918898b7047 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6840,6 +6840,10 @@ 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.

@@ -6873,6 +6877,13 @@ 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..fd0f82464f7d 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 = BIT(PSCI_1_3_HIBERNATE_TYPE_OFF);
+ break;
}
break;
case PSCI_1_0_FN_SYSTEM_SUSPEND:
@@ -392,6 +403,32 @@ 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);
+ if (arg != PSCI_1_3_HIBERNATE_TYPE_OFF) {
+ 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);
}
--
2.44.0