From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrey Smetanin Subject: Re: [PATCH v1] kvm/x86: Hyper-V tsc page setup Date: Fri, 22 Jan 2016 14:31:05 +0300 Message-ID: <56A212F9.4030800@virtuozzo.com> References: <1450949580-25759-1-git-send-email-asmetanin@virtuozzo.com> <56A1FF8F.3050701@redhat.com> <56A20131.8090102@virtuozzo.com> <56A20C30.4020608@redhat.com> Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , Roman Kagan , "Denis V. Lunev" , To: Paolo Bonzini , Return-path: Received: from mx2.parallels.com ([199.115.105.18]:38711 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752643AbcAVLbS (ORCPT ); Fri, 22 Jan 2016 06:31:18 -0500 In-Reply-To: <56A20C30.4020608@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 01/22/2016 02:02 PM, Paolo Bonzini wrote: > > > On 22/01/2016 11:15, Andrey Smetanin wrote: >>> >>> - unless KVM can use a master clock, it is incorrect to set up the TSC >>> page this way; the sequence needs to be 0xFFFFFFFF in that case >> 0xFFFFFFFF is not an invalid value for tsc page, >> see https://lkml.org/lkml/2015/11/2/655 > > oh, I see now. > >>> - writing the TSC page must be done while all VCPUs are stopped, because >>> the TSC page doesn't provide the possibility for the guest to retry in >>> the middle of an update (like seqcount in Linux doess) >> I think Windows guest gives tsc page address at boot time and protects >> against other vcpu's tsc page access. > > Sometimes the TSC is detected to be unstable and Linux switches to > another clocksource. At least in that case you can get a write to the > TSC page while the guest is running. Sorry, now I got it, you mean host TSC is unstable and we should mark guest tsc page invalid. Now I understand please ignore my prev. message. > > In that case it would be enough to write a zero to tsc_sequence, which > _can_ be done atomically while the guest is running. However, KVM > already has a mechanism to stop all VCPUs (KVM_REQ_MASTERCLOCK_UPDATE) > so we might as well use it. > > Paolo >