[PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs

On 31 July 2014 17:50, Christoffer Dall [off-list ref] wrote:

On Thu, Jul 31, 2014 at 05:45:28PM +0100, Peter Maydell wrote:

quoted

Consider the case where the reset state of the system is
"CPU 0 running, CPUs 1..N stopped", and we're doing an
incoming migration to a state where all CPUs are running.
In that case we'll be using this ioctl to clear the pause flag,
right? (We'll also obviously need to set the PC and other
register state correctly before resuming the guest.)

Doh, you're right, I somehow had it in my mind that when you send the
thread a signal, the pause flag would be cleared, but that goes against
the whole idea of a CPU being turned off for KVM.

But wouldn't we then have to also wake up the thread when clearing the
pause flag?  It feels strange that the ioctl can clear the pause flag,
but keep the thread on a wake-queue, and then userspace has to send the
thread a signal of some sort to wake it up?

I have no idea about the implementation, I just know what
the user-facing ABI ought to look like. In particular userspace
definitely shouldn't have to send the thread any kind of
signal, it should just use KVM_RUN as usual and that should
cause the vCPU to either remain powered-down or start
executing code, as appropriate for the state we've just set.

-- PMM