Re: [RFC PATCH 1/2] KVM: arm64: Add PSCI SYSTEM_OFF2 function for hibernation

[Marc Zyngier <maz@kernel.org>]

On Tue, 12 Mar 2024 13:51:28 +0000,
David Woodhouse <dwmw2@infradead.org> wrote:
> 
> 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/hyp/nvhe/psci-relay.c |  2 ++
>  arch/arm64/kvm/psci.c                | 37 ++++++++++++++++++++++++++++
>  include/uapi/linux/kvm.h             |  1 +
>  include/uapi/linux/psci.h            |  5 ++++
>  8 files changed, 69 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index bd93cafd3e4e..f5963c3770a5 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

Checking that PSCI 1.3 is enabled for the guest should be enough, no?
I don't think providing yet another level of optionally brings us
much, other than complexity.

> +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 21c57b812569..d6da0eb1c236 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -274,6 +274,8 @@ struct kvm_arch {
>  #define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		6
>  	/* Initial ID reg values loaded */
>  #define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		7
> +	/* PSCI SYSTEM_OFF2 (hibernate) enabled for the guest */
> +#define KVM_ARCH_FLAG_SYSTEM_OFF2_ENABLED		8
>  	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 a25265aca432..1c58762272eb 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];
>  
> @@ -238,6 +242,7 @@ 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/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> index d57bcb6ab94d..0d4bea0b9ca2 100644
> --- a/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> +++ b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
> @@ -264,6 +264,8 @@ static unsigned long psci_1_0_handler(u64 func_id, struct kvm_cpu_context *host_
>  	switch (func_id) {
>  	case PSCI_1_0_FN_PSCI_FEATURES:
>  	case PSCI_1_0_FN_SET_SUSPEND_MODE:
> +	case PSCI_1_3_FN_SYSTEM_OFF2:
> +	case PSCI_1_3_FN64_SYSTEM_OFF2:

nit: order by version number.

>  	case PSCI_1_1_FN64_SYSTEM_RESET2:
>  		return psci_forward(host_ctxt);
>  	case PSCI_1_0_FN64_SYSTEM_SUSPEND:
> 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;

Testing the PSCI version should be enough (minor >= 3). Same thing
goes the the capability: checking that the host supports 1.3 should be
enough.

	M.

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