From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 0/5 V4] Avoid soft lockup message when KVM is stopped by host Date: Thu, 1 Dec 2011 19:25:58 -0200 Message-ID: <20111201212558.GC25290@amt.cnet> References: <1322602539-27004-1-git-send-email-emunson@mgebm.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx1.redhat.com ([209.132.183.28]:16774 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754243Ab1LAV1O (ORCPT ); Thu, 1 Dec 2011 16:27:14 -0500 Content-Disposition: inline In-Reply-To: <1322602539-27004-1-git-send-email-emunson@mgebm.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Eric B Munson Cc: avi@redhat.com, mingo@redhat.com, hpa@zytor.com, arnd@arndb.de, ryanh@linux.vnet.ibm.com, aliguori@us.ibm.com, jeremy.fitzhardinge@citrix.com, kvm@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org On Tue, Nov 29, 2011 at 04:35:34PM -0500, Eric B Munson wrote: > Changes from V3: > Include CC's on patch 3 > Drop clear flag ioctl and have the watchdog clear the flag when it is reset > > Changes from V2: > A new kvm functions defined in kvm_para.h, the only change to pvclock is the > initial flag definition > > Changes from V1: > (Thanks Marcelo) > Host code has all been moved to arch/x86/kvm/x86.c > KVM_PAUSE_GUEST was renamed to KVM_GUEST_PAUSED > > When a guest kernel is stopped by the host hypervisor it can look like a soft > lockup to the guest kernel. This false warning can mask later soft lockup > warnings which may be real. This patch series adds a method for a host > hypervisor to communicate to a guest kernel that it is being stopped. The > final patch in the series has the watchdog check this flag when it goes to > issue a soft lockup warning and skip the warning if the guest knows it was > stopped. > > It was attempted to solve this in Qemu, but the side effects of saving and > restoring the clock and tsc for each vcpu put the wall clock of the guest behind > by the amount of time of the pause. This forces a guest to have ntp running > in order to keep the wall clock accurate. Looks good to me.