From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59619) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Y9GzF-0003BH-9h for qemu-devel@nongnu.org; Thu, 08 Jan 2015 12:35:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Y9Gz6-00063P-Eo for qemu-devel@nongnu.org; Thu, 08 Jan 2015 12:35:09 -0500 Received: from e33.co.us.ibm.com ([32.97.110.151]:37555) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Y9Gz6-00062k-7x for qemu-devel@nongnu.org; Thu, 08 Jan 2015 12:35:00 -0500 Received: from /spool/local by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 8 Jan 2015 10:34:59 -0700 From: Michael Roth Date: Thu, 8 Jan 2015 11:33:12 -0600 Message-Id: <1420738472-23267-9-git-send-email-mdroth@linux.vnet.ibm.com> In-Reply-To: <1420738472-23267-1-git-send-email-mdroth@linux.vnet.ibm.com> References: <1420738472-23267-1-git-send-email-mdroth@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH 08/88] 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: qemu-stable@nongnu.org From: Eduardo Habkost 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 Gibuła Cc: Marcelo Tosatti Cc: Paolo Bonzini Signed-off-by: Paolo Bonzini (cherry picked from commit 1154d84dcc5f46e83db94281d071775819dd8884) Signed-off-by: Michael Roth --- 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, int running, } 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 CPUState + * is supposed to always match the VCPU state on the kernel side. + * + * In practice, calling cpu_synchronize_state() too soon will load the + * kernel-side APIC state into X86CPU.apic_state too early, APIC state + * won't be reloaded later because CPUState.vcpu_dirty==true, and + * outdated APIC state may be migrated to another host. + * + * The real fix would be to make sure outdated APIC state is read + * 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 = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data); if (ret < 0) { fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret)); -- 1.9.1