Re: [PATCH v3 0/3] KVM: Set vcpu->preempted/ready iff scheduled out while running

On Tue, Jun 18, 2024 at 2:41 PM Sean Christopherson [off-list ref] wrote:

On Fri, 03 May 2024 11:17:31 -0700, David Matlack wrote:

quoted

This series changes KVM to mark a vCPU as preempted/ready if-and-only-if
it's scheduled out while running. i.e. Do not mark a vCPU
preempted/ready if it's scheduled out during a non-KVM_RUN ioctl() or
when userspace is doing KVM_RUN with immediate_exit=true.

This is a logical extension of commit 54aa83c90198 ("KVM: x86: do not
set st->preempted when going back to user space"), which  stopped
marking a vCPU as preempted when returning to userspace. But if userspace
invokes a KVM vCPU ioctl() that gets preempted, the vCPU will be marked
preempted/ready. This is arguably incorrect behavior since the vCPU was
not actually preempted while the guest was running, it was preempted
while doing something on behalf of userspace.

[...]

Applied to kvm-x86 generic, with minor changelog tweaks (me thinks you've been
away from upstream too long ;-) ).  Thanks!

Thanks for the cleanups. Looks like you replaced "[Tt]his commit"
throughout. Anything else (so I can avoid the same mistakes in the
future)?

[1/3] KVM: Introduce vcpu->wants_to_run
      https://github.com/kvm-x86/linux/commit/a6816314af57
[2/3] KVM: Ensure new code that references immediate_exit gets extra scrutiny
      https://github.com/kvm-x86/linux/commit/4b23e0c199b2
[3/3] KVM: Mark a vCPU as preempted/ready iff it's scheduled out while running
      https://github.com/kvm-x86/linux/commit/118964562969

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