Allow userspace to request handling PSCI calls from guests. Our goal is to enable a vCPU hot-add solution for Arm where the VMM presents possible resources to the guest at boot, and controls which vCPUs can be brought up by allowing or denying PSCI CPU_ON calls. Passing HVC and PSCI to userspace has been discussed on the list in the context of vCPU hot-add [1,2] but it can also be useful for implementing other SMCCC and vendor hypercalls [3,4,5]. Patches 1-3 allow userspace to request WFI to be executed in KVM. That way the VMM can easily implement the PSCI CPU_SUSPEND function, which is mandatory from PSCI v0.2 onwards (even if it doesn't have a more useful implementation than WFI, natively available to the guest). Patch 4 lets userspace request any HVC that isn't handled by KVM, and patch 5 lets userspace request PSCI calls, disabling in-kernel PSCI handling. I'm focusing on the PSCI bits, but a complete prototype of vCPU hot-add for arm64 on Linux and QEMU, most of it from Salil and James, is available at [6]. [1] https://lore.kernel.org/kvmarm/82879258-46a7-a6e9-ee54-fc3692c1cdc3@xxxxxxx/ [2] https://lore.kernel.org/linux-arm-kernel/20200625133757.22332-1-salil.mehta@xxxxxxxxxx/ (Followed by KVM forum and Linaro Open discussions) [3] https://lore.kernel.org/linux-arm-kernel/f56cf420-affc-35f0-2355-801a924b8a35@xxxxxxx/ [4] https://lore.kernel.org/kvm/bf7e83f1-c58e-8d65-edd0-d08f27b8b766@xxxxxxx/ [5] https://lore.kernel.org/kvm/1569338454-26202-2-git-send-email-guoheyi@xxxxxxxxxx/ [6] https://jpbrucker.net/git/linux/log/?h=cpuhp/devel https://jpbrucker.net/git/qemu/log/?h=cpuhp/devel Jean-Philippe Brucker (5): KVM: arm64: Replace power_off with mp_state in struct kvm_vcpu_arch KVM: arm64: Move WFI execution to check_vcpu_requests() KVM: arm64: Allow userspace to request WFI KVM: arm64: Pass hypercalls to userspace KVM: arm64: Pass PSCI calls to userspace Documentation/virt/kvm/api.rst | 46 +++++++++++++++---- Documentation/virt/kvm/arm/psci.rst | 1 + arch/arm64/include/asm/kvm_host.h | 10 +++- include/kvm/arm_hypercalls.h | 1 + include/kvm/arm_psci.h | 4 ++ include/uapi/linux/kvm.h | 3 ++ arch/arm64/kvm/arm.c | 71 +++++++++++++++++++++-------- arch/arm64/kvm/handle_exit.c | 3 +- arch/arm64/kvm/hypercalls.c | 28 +++++++++++- arch/arm64/kvm/psci.c | 69 ++++++++++++++-------------- 10 files changed, 170 insertions(+), 66 deletions(-) -- 2.31.1
