On 31 July 2014 17:50, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: > On Thu, Jul 31, 2014 at 05:45:28PM +0100, Peter Maydell wrote: >> 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html