The PSCI v1.3 spec (https://developer.arm.com/documentation/den0022, currently in Alpha state, hence 'RFC') adds support for a SYSTEM_OFF2 function enabling a HIBERNATE_OFF state which is analogous to ACPI S4. 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). This adds support for it to KVM, exactly the same way as the existing support for SYSTEM_RESET2 as added in commits d43583b890e7 ("KVM: arm64: Expose PSCI SYSTEM_RESET2 call to the guest") and 34739fd95fab ("KVM: arm64: Indicate SYSTEM_RESET2 in kvm_run::system_event flags field"). Back then, KVM was unconditionally bumped to expose PSCI v1.1. This means that a kernel upgrade causes guest visible behaviour changes without any explicit opt-in from the VMM, which is... unconventional. In some cases, a PSCI update isn't just about new optional calls; PSCI v1.2 for example adds a new permitted error return from the existing CPU_ON function. There *is* a way for a VMM to opt *out* of newer PSCI versions... by setting a per-vCPU "special" register that actually ends up setting the PSCI version KVM-wide. Quite why this isn't just a simple KVM_CAP, I have no idea. There *is* a KVM_CAP_ARM_PSCI_0_2 but that's just for 0.1 vs. 0.2+, not the specific v0.2+ version that's exposed. Since the SYSTEM_OFF2 call is optional and discoverable through the PSCI_FEATURES call, I'm electing not to touch the PSCI versioning awfulness at all. Like the existing SYSTEM_RESET2, there's a KVM_CAP to enable it explicitly (as it's an optional call even in v1.3), and like the existing SYSTEM_RESET2 it doesn't depend on the advertised PSCI version. For the guest side, add a new SYS_OFF_MODE_POWER_OFF handler with higher priority than the EFI one, but which *only* triggers when there's a hibernation in progress. There are other ways to do this (see the commit message for more details) but this seemed like the simplest. Version 2 of the patch series splits out the psci.h definitions into a separate commit (a dependency for both the guest and KVM side), and adds definitions for the other new functions added in v1.3. It also moves the pKVM psci-relay support to a separate commit; although in arch/arm64/kvm that's actually about the *guest* side of SYSTEM_OFF2 (i.e. using it from the host kernel, relayed through nVHE). David Woodhouse (4): firmware/psci: Add definitions for PSCI v1.3 specification (ALPHA) KVM: arm64: Add PSCI SYSTEM_OFF2 function for hibernation KVM: arm64: nvhe: Pass through PSCI v1.3 SYSTEM_OFF2 call arm64: Use SYSTEM_OFF2 PSCI call to power off for hibernate 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 ++++++++++++++++++++++++++++++++++++ drivers/firmware/psci/psci.c | 35 ++++++++++++++++++++++++++++++++++ include/uapi/linux/kvm.h | 1 + include/uapi/linux/psci.h | 20 +++++++++++++++++++ kernel/power/hibernate.c | 5 ++++- 10 files changed, 123 insertions(+), 1 deletion(-)
