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

[Oliver Upton]

Hi,

On Tue, Mar 12, 2024 at 01:51:28PM +0000, David Woodhouse 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.

Have you considered doing the PSCI implementation in userspace? The
SMCCC filter [*] was added for this exact purpose. There are other
features being done in userspace (e.g. vCPU hotplug) built on
intercepting hypercalls, this seems to be a reasonable candidate too.

[*] https://docs.kernel.org/virt/kvm/devices/vm.html#attribute-kvm-arm-vm-smccc-filter-w-o

-- 
Thanks,
Oliver