Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751985AbaGaQyU (ORCPT ); Thu, 31 Jul 2014 12:54:20 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:55529 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751292AbaGaQyT (ORCPT ); Thu, 31 Jul 2014 12:54:19 -0400 MIME-Version: 1.0 In-Reply-To: <20140731165006.GL11610@cbox> References: <1404914112-7298-1-git-send-email-alex.bennee@linaro.org> <20140731143538.GI11610@cbox> <87mwbpimgz.fsf@linaro.org> <20140731163805.GK11610@cbox> <20140731165006.GL11610@cbox> From: Peter Maydell Date: Thu, 31 Jul 2014 17:53:56 +0100 Message-ID: Subject: Re: [PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs To: Christoffer Dall Cc: =?UTF-8?B?QWxleCBCZW5uw6ll?= , kvm-devel , Catalin Marinas , Will Deacon , open list , Gleb Natapov , Paolo Bonzini , "kvmarm@lists.cs.columbia.edu" , arm-mail-list Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31 July 2014 17:50, Christoffer Dall 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 linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/