From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robbie Dinn Subject: Re: wget and Zope crashes on post-2.0.6 -testing Date: Fri, 10 Jun 2005 20:52:02 +0100 Message-ID: <42A9EF62.4050506@microbus.com> References: <20050608214244.GF12001@tpkurt.garloff.de> <9c5e466efcd5d7dfb6487487187d2c3e@cl.cam.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9c5e466efcd5d7dfb6487487187d2c3e@cl.cam.ac.uk> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Hi all Keir Fraser wrote: > > When set it causes a fault whenever the FPU is accessed. We use it to > lazily initialise the FPU for the currently running process. At > context-switch time we look at the process we are descheduling and, if > it hasn;t used the FPU in its time slice, we don;t save FPU state and we > don;t set the TS bit (because we assume it must be already set). > > The last point is where we can fall down: if the TS bit in fact *isn;t* > set, then we are screwed for all time. The kernel will never realise a > process is using the FPU because we will never take the TS fault, > because the TS bit is clear. Thus state doesn;t get saved/restored > during context switch and the TS bit never gets set. So its a self > perpetuating state once you're in it. I have an end user question rather than a developers Q. Say I have an xen machine with several domains, some with kernels that have the FPU bug fix and some without. Can a domain with the buggy kernel upset a domain with a bug free kernel? Or does this just affect processes within one domain? I might want to be a bit more hasty in upgrading all the kernels if a buggy kernel/domain can upset a good kernel/domain.