From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42989) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XlLhW-0001el-Eg for qemu-devel@nongnu.org; Mon, 03 Nov 2014 12:46:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XlLhS-0005NV-0O for qemu-devel@nongnu.org; Mon, 03 Nov 2014 12:45:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40883) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XlLhR-0005NL-Oy for qemu-devel@nongnu.org; Mon, 03 Nov 2014 12:45:53 -0500 From: Eduardo Habkost Date: Mon, 3 Nov 2014 15:45:34 -0200 Message-Id: <1415036734-24310-1-git-send-email-ehabkost@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PATCH] kvmclock: Add comment explaining why we need cpu_clean_all_dirty() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Andrey Korolyov , =?UTF-8?q?Marcin=20Gibu=C5=82a?= , Marcelo Tosatti Try to explain why commit 317b0a6d8ba44e9bf8f9c3dbd776c4536843d82c needed a cpu_clean_all_dirty() call just after calling cpu_synchronize_all_states(). Signed-off-by: Eduardo Habkost Cc: Andrey Korolyov Cc: Marcin Gibu=C5=82a Cc: Marcelo Tosatti Cc: Paolo Bonzini --- hw/i386/kvm/clock.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c index 1ac60d6..58be2bd 100644 --- a/hw/i386/kvm/clock.c +++ b/hw/i386/kvm/clock.c @@ -127,7 +127,21 @@ static void kvmclock_vm_state_change(void *opaque, i= nt running, } =20 cpu_synchronize_all_states(); + /* In theory, the cpu_synchronize_all_states() call above wouldn= 't + * affect the rest of the code, as the VCPU state inside CPUStat= e + * is supposed to always match the VCPU state on the kernel side. + * + * In practice, calling cpu_synchronize_state() too soon will lo= ad the + * kernel-side APIC state into X86CPU.apic_state too early, APIC= state + * won't be reloaded later because CPUState.vcpu_dirty=3D=3Dtrue= , and + * outdated APIC state may be migrated to another host. + * + * The real fix would be to make sure outdated APIC state is rea= d + * from the kernel again when necessary. While this is not fixed= , we + * need the cpu_clean_all_dirty() call below. + */ cpu_clean_all_dirty(); + ret =3D kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data); if (ret < 0) { fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret))= ; --=20 1.9.3