On Thu, Mar 7, 2024 at 8:35 AM David Matlack <dmatlack@xxxxxxxxxx> wrote:
>
> 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.
>
> Commit 54aa83c90198 ("KVM: x86: do not set st->preempted when going back
> to user space") stopped marking a vCPU as preempted when returning to
> userspace, but if userspace then 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.
>
> This commit also avoids KVM dirtying guest memory after userspace has
> paused vCPUs, e.g. for Live Migration, which allows userspace to collect
> the final dirty bitmap before or in parallel with saving vCPU state
> without having to worry about saving vCPU state triggering writes to
> guest memory.
>
> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
Gentle ping.
