From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/1] Disable GUEST_INTR_STATE_STI flag before injecting NMI to guest on VMX Date: Fri, 27 Aug 2010 18:50:19 +0300 Message-ID: <4C77DEBB.9040801@redhat.com> References: <1282853162-16925-1-git-send-email-Jes.Sorensen@redhat.com> <1282853162-16925-2-git-send-email-Jes.Sorensen@redhat.com> <4C7776F9.4070306@siemens.com> <4C7777CA.4010208@redhat.com> <4C7779D2.9090902@siemens.com> <4C77895A.1000708@redhat.com> <4C779C3D.2070700@siemens.com> <4C77C49A.9000600@redhat.com> <4C77C812.4040103@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Jes Sorensen , "kvm@vger.kernel.org" , "gleb@redhat.com" , Joerg Roedel To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:48426 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754682Ab0H0Pu2 (ORCPT ); Fri, 27 Aug 2010 11:50:28 -0400 In-Reply-To: <4C77C812.4040103@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/27/2010 05:13 PM, Jan Kiszka wrote: > >> I forgot them already. What was that, exception during IRET? > Exception during IRET or any instruction under the interrupt shadow will > push the TF we set to step over this issue on the guest stack. We do not > intercept all the possible exceptions, so we can leak TF. Moreover, > multiplexing TF users is currently imperfect on AMD but, before fixing > that, we have to think about the approach in general. Thanks. I think those are all solvable. The key IMO is to take a state based approach to host bits - instead of setting or clearing a bit in response to an event, use the event as a trigger for recalculation of the bit's value. This works for bits which have multiple uses, and for recovery from KVM_SET_*. For guest bits which are needed by the host we also have a working approach - when the bit is overloaded, trap all instructions that can see it, as in CR0.TS. It may take some work but I think we can achieve 100% accuracy without making the code unmaintainable. >> I'd really like to avoid the timer. But I forgot all the details around >> this, I'll have to re-learn them so I can actually compare the two options. >> > Hope the above helps you to get on track, otherwise drop more questions. > Also putting Joerg on CC (in the futile hope that the longer the CC list > is, the lesser the pain becomes for each individual). I think I got it. And I also think we need to start documenting these invariants, to make it easier for people to see the method in all that chaos. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.