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

From: Jean-Philippe Brucker
Date: Tue Jun 08 2021 - 11:54:21 EST


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(-)

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2.31.1