[RFC,kvmtool,0/5] ARM: Implement PSCI SYSTEM_SUSPEND

Message

Oliver Upton March 11, 2022, 5:57 p.m. UTC

This is a prototype for supporting KVM_CAP_ARM_SYSTEM_SUSPEND on
kvmtool. The capability allows userspace to expose the SYSTEM_SUSPEND
PSCI call to its guests.

Implement SYSTEM_SUSPEND using KVM_MP_STATE_SUSPENDED, which emulates
the execution of a WFI instruction in the kernel. Resume the guest when
a wakeup event is recognized and reset it to the requested entry address
and context ID.

Patches 2-4 are small reworks to more easily shoehorn PSCI support into
kvmtool.

Patch 5 adds some SMCCC handlers and makes use of them to implement PSCI
SYSTEM_SUSPEND. For now, just check the bare-minimum, that all vCPUs
besides the caller have stopped. There are also checks that can be made
against the requested entry address, but they are at the discretion of
the implementation.

Tested with 'echo mem > /sys/power/state' to see that the vCPU is in
fact placed in a suspended state for the PSCI call. Hacked the switch
statement to fall through to WAKEUP immediately after to verify the vCPU
is set up correctly for resume.

It would be nice if kvmtool actually provided a device good for wakeups,
since the RTC implementation has omitted any interrupt support.

kernel changes: http://lore.kernel.org/r/[e-mail]

Oliver Upton (5):
  TESTONLY: Sync KVM headers with pending changes
  Allow architectures to hook KVM_EXIT_SYSTEM_EVENT
  ARM: Stash vcpu_init in the vCPU structure
  ARM: Add a helper to re-init a vCPU
  ARM: Implement PSCI SYSTEM_SUSPEND

 arm/aarch32/kvm-cpu.c                 | 72 ++++++++++++++++++++
 arm/aarch64/kvm-cpu.c                 | 66 +++++++++++++++++++
 arm/include/arm-common/kvm-cpu-arch.h | 23 ++++---
 arm/kvm-cpu.c                         | 95 ++++++++++++++++++++++++++-
 arm/kvm.c                             |  9 +++
 include/kvm/kvm-cpu.h                 |  1 +
 include/linux/kvm.h                   | 21 ++++++
 kvm-cpu.c                             |  8 +++
 8 files changed, 283 insertions(+), 12 deletions(-)

Comments

Will Deacon May 6, 2022, 1:01 p.m. UTC | #1

On Fri, Mar 11, 2022 at 05:57:12PM +0000, Oliver Upton wrote:
> This is a prototype for supporting KVM_CAP_ARM_SYSTEM_SUSPEND on
> kvmtool. The capability allows userspace to expose the SYSTEM_SUSPEND
> PSCI call to its guests.
> 
> Implement SYSTEM_SUSPEND using KVM_MP_STATE_SUSPENDED, which emulates
> the execution of a WFI instruction in the kernel. Resume the guest when
> a wakeup event is recognized and reset it to the requested entry address
> and context ID.
> 
> Patches 2-4 are small reworks to more easily shoehorn PSCI support into
> kvmtool.
> 
> Patch 5 adds some SMCCC handlers and makes use of them to implement PSCI
> SYSTEM_SUSPEND. For now, just check the bare-minimum, that all vCPUs
> besides the caller have stopped. There are also checks that can be made
> against the requested entry address, but they are at the discretion of
> the implementation.
> 
> Tested with 'echo mem > /sys/power/state' to see that the vCPU is in
> fact placed in a suspended state for the PSCI call. Hacked the switch
> statement to fall through to WAKEUP immediately after to verify the vCPU
> is set up correctly for resume.
> 
> It would be nice if kvmtool actually provided a device good for wakeups,
> since the RTC implementation has omitted any interrupt support.
> 
> kernel changes: http://lore.kernel.org/r/[e-mail]
> 
> Oliver Upton (5):
>   TESTONLY: Sync KVM headers with pending changes
>   Allow architectures to hook KVM_EXIT_SYSTEM_EVENT
>   ARM: Stash vcpu_init in the vCPU structure
>   ARM: Add a helper to re-init a vCPU
>   ARM: Implement PSCI SYSTEM_SUSPEND
> 
>  arm/aarch32/kvm-cpu.c                 | 72 ++++++++++++++++++++
>  arm/aarch64/kvm-cpu.c                 | 66 +++++++++++++++++++
>  arm/include/arm-common/kvm-cpu-arch.h | 23 ++++---
>  arm/kvm-cpu.c                         | 95 ++++++++++++++++++++++++++-
>  arm/kvm.c                             |  9 +++
>  include/kvm/kvm-cpu.h                 |  1 +
>  include/linux/kvm.h                   | 21 ++++++
>  kvm-cpu.c                             |  8 +++
>  8 files changed, 283 insertions(+), 12 deletions(-)

Looks like the kernel-side changes are queued now, so please can you resend
this series? I also think you can drop the AArch32 support, unless you see a
compelling reason for it?

Will

Oliver Upton May 6, 2022, 7:18 p.m. UTC | #2

Hi Will,

On Fri, May 6, 2022 at 6:01 AM Will Deacon <[e-mail]> wrote:
>
> Looks like the kernel-side changes are queued now, so please can you resend
> this series? I also think you can drop the AArch32 support, unless you see a
> compelling reason for it?

You bet. I was going to wait for 5.19-rc1 just for the dust to settle
and get a stable number for the UAPI bits. I think the ARM changes
have some light conflicts with SEV work in Paolo's tree.

All for dropping AArch32, means less work for me :-P

--
Thanks,
Oliver