[RFC PATCH 0/5] KVM: arm64: Pass PSCI to userspace

[Jean-Philippe Brucker]

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@arm.com/
[2] https://lore.kernel.org/linux-arm-kernel/20200625133757.22332-1-salil.mehta@huawei.com/
    (Followed by KVM forum and Linaro Open discussions)
[3] https://lore.kernel.org/linux-arm-kernel/f56cf420-affc-35f0-2355-801a924b8a35@arm.com/
[4] https://lore.kernel.org/kvm/bf7e83f1-c58e-8d65-edd0-d08f27b8b766@arm.com/
[5] https://lore.kernel.org/kvm/1569338454-26202-2-git-send-email-guoheyi@huawei.com/
[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