Re: [RFC PATCH v3 3/5] KVM: arm64: Add PSCI v1.3 SYSTEM_OFF2 function for hibernation

[Marc Zyngier]

On Tue, 19 Mar 2024 12:59:04 +0000,
David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote:
> 
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> 
> 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.
> 
> Although this new feature is inflicted unconditionally on unexpecting
> userspace, it ought to be mostly 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@xxxxxxxxxxxx>
> ---
>  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 0b5a33ee71ee..ba4ddb13e253 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 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 f689ef3f2f10..7acf07900c08 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 (minor >= 3)
> +				val = 1UL << PSCI_1_3_HIBERNATE_TYPE_OFF;
> +			break;
>  		case PSCI_1_1_FN_SYSTEM_RESET2:
>  		case PSCI_1_1_FN64_SYSTEM_RESET2:

nit: please keep the switch ordered by version number.

>  			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 (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;
>  	case PSCI_1_1_FN_SYSTEM_RESET2:
>  		kvm_psci_narrow_to_32bit(vcpu);
>  		fallthrough;

Same thing here.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.