[RFC PATCH v2 2/4] KVM: arm64: Add PSCI SYSTEM_OFF2 function for hibernation

David Woodhouse
2024-03-18T16:47:09Z

From: David Woodhouse <dwmw@amazon.co.uk>

The PSCI v1.3 specification (alpha) 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).

The beta version will be changed to say that PSCI_FEATURES returns a bit
mask of the supported hibernate types, which is implemented here.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
Documentation/virt/kvm/api.rst | 11 +++++++++
arch/arm64/include/asm/kvm_host.h | 2 ++
arch/arm64/include/uapi/asm/kvm.h | 6 +++++
arch/arm64/kvm/arm.c | 5 +++++
arch/arm64/kvm/psci.c | 37 +++++++++++++++++++++++++++++++
include/uapi/linux/kvm.h | 1 +
6 files changed, 62 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 0b5a33ee71ee..ff061b6a2393 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6761,6 +6761,10 @@ 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.

@@ -6794,6 +6798,13 @@ 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 with the
+KVM_CAP_ARM_SYSTEM_OFF2 VM capability. 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/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 6883963bbc3a..6ed05791afdb 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -299,6 +299,8 @@ struct kvm_arch {
#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED 7
/* Fine-Grained UNDEF initialised */
#define KVM_ARCH_FLAG_FGU_INITIALIZED 8
+ /* PSCI SYSTEM_OFF2 (hibernate) enabled for the guest */
+#define KVM_ARCH_FLAG_SYSTEM_OFF2_ENABLED 9
unsigned long flags;

/* VM-wide vCPU feature set */
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/arm.c b/arch/arm64/kvm/arm.c
index 3dee5490eea9..47d23064d6f7 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -98,6 +98,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
r = 0;
set_bit(KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED, &kvm->arch.flags);
break;
+ case KVM_CAP_ARM_SYSTEM_OFF2:
+ r = 0;
+ set_bit(KVM_ARCH_FLAG_SYSTEM_OFF2_ENABLED, &kvm->arch.flags);
+ break;
case KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE:
new_cap = cap->args[0];

@@ -243,6 +247,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_VCPU_ATTRIBUTES:
case KVM_CAP_PTP_KVM:
case KVM_CAP_ARM_SYSTEM_SUSPEND:
+ case KVM_CAP_ARM_SYSTEM_OFF2:
case KVM_CAP_IRQFD_RESAMPLE:
case KVM_CAP_COUNTER_OFFSET:
r = 1;
diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
index 1f69b667332b..59570eea8aa7 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);
@@ -353,6 +359,11 @@ static int kvm_psci_1_x_call(struct kvm_vcpu *vcpu, u32 minor)
if (test_bit(KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED, &kvm->arch.flags))
val = 0;
break;
+ case PSCI_1_3_FN_SYSTEM_OFF2:
+ case PSCI_1_3_FN64_SYSTEM_OFF2:
+ if (test_bit(KVM_ARCH_FLAG_SYSTEM_OFF2_ENABLED, &kvm->arch.flags))
+ val = 1UL << PSCI_1_3_HIBERNATE_TYPE_OFF;
+ break;
case PSCI_1_1_FN_SYSTEM_RESET2:
case PSCI_1_1_FN64_SYSTEM_RESET2:
if (minor >= 1)
@@ -374,6 +385,32 @@ static int kvm_psci_1_x_call(struct kvm_vcpu *vcpu, u32 minor)
return 0;
}
break;
+ case PSCI_1_3_FN_SYSTEM_OFF2:
+ kvm_psci_narrow_to_32bit(vcpu);
+ fallthrough;
+ case PSCI_1_3_FN64_SYSTEM_OFF2:
+ if (!test_bit(KVM_ARCH_FLAG_SYSTEM_OFF2_ENABLED, &kvm->arch.flags))
+ 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_OFF 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;
case PSCI_1_1_FN_SYSTEM_RESET2:
kvm_psci_narrow_to_32bit(vcpu);
fallthrough;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2190adbe3002..caa3845b80d6 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -917,6 +917,7 @@ struct kvm_enable_cap {
#define KVM_CAP_MEMORY_ATTRIBUTES 233
#define KVM_CAP_GUEST_MEMFD 234
#define KVM_CAP_VM_TYPES 235
+#define KVM_CAP_ARM_SYSTEM_OFF2 236

struct kvm_irq_routing_irqchip {
__u32 irqchip;
--
2.44.0