On Thu, 11 Sept 2025 at 16:59, Sebastian Ott <sebott@xxxxxxxxxx> wrote: > > On Thu, 11 Sep 2025, Peter Maydell wrote: > > On Thu, 11 Sept 2025 at 15:49, Sebastian Ott <sebott@xxxxxxxxxx> wrote: > >> > >> This series adds a vcpu knob to request a specific PSCI version > >> from KVM via the KVM_REG_ARM_PSCI_VERSION FW register. > >> > >> Note: in order to support PSCI v0.1 we need to drop vcpu > >> initialization with KVM_CAP_ARM_PSCI_0_2 in that case. > >> Alternatively we could limit support to versions >=0.2 . > >> > >> Sebastian Ott (2): > >> target/arm/kvm: add constants for new PSCI versions > >> target/arm/kvm: add kvm-psci-version vcpu property > > > > Could we have some rationale, please? What's the use case > > where you might need to specify a particular PSCI version? > > The use case is migrating between different host kernel versions. > Per default the kernel reports the latest PSCI version in the > KVM_REG_ARM_PSCI_VERSION register (for KVM_CAP_ARM_PSCI_0_2) - > when that differs between source and target a migration will fail. > > This property allows to request a PSCI version that is supported by > both sides. Specifically I want to support migration between host > kernels with and without the following Linux commit: > 8be82d536a9f KVM: arm64: Add support for PSCI v1.2 and v1.3 So if the destination kernel is post that commit and the source kernel pre-dates it, do we fail migration? Or is this only a migration failure when the destination doesn't support the PSCI version we defaulted to at the source end? thanks -- PMM
