From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: Add three MSRs to the list of ignored MSRs Date: Fri, 15 Apr 2016 12:48:01 +0200 Message-ID: <5710C6E1.2020802@redhat.com> References: <1460626109-24343-1-git-send-email-shuai.ruan@linux.intel.com> <20160414133332.GA3350@potion.brq.redhat.com> <570FAC6F.10704@redhat.com> <20160414162907.GB3350@potion.brq.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Shuai Ruan , kvm@vger.kernel.org, allen.m.kay@intel.com To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Return-path: Received: from mx1.redhat.com ([209.132.183.28]:57685 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752233AbcDOKsJ (ORCPT ); Fri, 15 Apr 2016 06:48:09 -0400 In-Reply-To: <20160414162907.GB3350@potion.brq.redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 14/04/2016 18:29, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > I don't see that as a compromise. igd would fail even if we fixed th= e > host side, so we'll have problems regardless of what we do. Would it? I suppose that Shuai tested his patch. > We have a bug, because certain v/f/m/s implies some features (MSRs, > constant_tsc, ...) and those aren't emulated. >=20 > I do agree that we don't want to fix the bug, either by whitelisting = and > emulating features that makes little sense in virt or by forcing gues= ts > to adopt new v/f/m/s (the latter option is more reasonable), Well, the Pentium was the last processor without MSRs. :) More code would break if you set f=3D5 than if you return a bogus value for MSR_PLATFORM_INFO. This is the compromise I was referring to. The only solution is to bug Intel to add CPUID bits even for non-architectural features. Then _if_ the CPUID bit is there you use f/m/s to find the details of the feature. Intel likes to get feedback from us and we did provide such feedback. The problem is that the 2-3 years that pass between giving feedback and getting our hands on the silicon. Paolo > because > rare occurences of the bug take *much* less work to fix on the guest > side. (The only part I'm concerned about is that we don't have a goo= d > excuse for some guest errors ...)