From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [PATCH 14/18] Fix a possible backwards warp of kvmclock Date: Wed, 14 Jul 2010 22:37:00 -0400 Message-ID: <4C3E744C.7060402@redhat.com> References: <1278987938-23873-1-git-send-email-zamsden@redhat.com> <1278987938-23873-15-git-send-email-zamsden@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: KVM , Avi Kivity , Marcelo Tosatti , Glauber Costa , Linux-kernel To: Zachary Amsden Return-path: In-Reply-To: <1278987938-23873-15-git-send-email-zamsden@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 07/12/2010 10:25 PM, Zachary Amsden wrote: > Kernel time, which advances in discrete steps may progress much slower > than TSC. As a result, when kvmclock is adjusted to a new base, the > apparent time to the guest, which runs at a much higher, nsec scaled > rate based on the current TSC, may have already been observed to have > a larger value (kernel_ns + scaled tsc) than the value to which we are > setting it (kernel_ns + 0). > > We must instead compute the clock as potentially observed by the guest > for kernel_ns to make sure it does not go backwards. > > Signed-off-by: Zachary Amsden Acked-by: Rik van Riel -- All rights reversed