From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] Re: [PATCH 2/2] introduce -cpu host target Date: Wed, 24 Jun 2009 20:46:13 +0300 Message-ID: <4A426665.1030506@redhat.com> References: <1245707277-769-1-git-send-email-andre.przywara@amd.com> <4A41F7EC.2000305@redhat.com> <5b31733c0906241037t54706611w19eeb2f27f8e63f3@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Andre Przywara , aliguori@us.ibm.com, qemu-devel@nongnu.org, kvm@vger.kernel.org To: Filip Navara Return-path: Received: from mx2.redhat.com ([66.187.237.31]:40977 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752740AbZFXRqH (ORCPT ); Wed, 24 Jun 2009 13:46:07 -0400 In-Reply-To: <5b31733c0906241037t54706611w19eeb2f27f8e63f3@mail.gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 06/24/2009 08:37 PM, Filip Navara wrote: > On Wed, Jun 24, 2009 at 11:54 AM, Avi Kivity wrote: > >> On 06/23/2009 12:47 AM, Andre Przywara wrote: >> >>> Should we ignore unhandled MSRs like QEMU or Xen do? >>> >>> >> Ignoring unhandled msrs is dangerous. If a write has some effect the guest >> depends on, and we're not emulating that effect, the guest will fail. >> Similarly if you don't know what a register mean, who knows what returning >> zero for a read will do. >> > > It is definitely a bad idea to ignore unknown MSRs. Kernel patch > protection scheme used by certain operating system depend on them to > work properly and it's pretty hard to debug when you don't know what > failed (the MSR read in this case). > > http://www.uninformed.org/?v=3&a=3 > http://www.uninformed.org/?v=6&a=1 > http://www.uninformed.org/?v=8&a=5 > http://en.wikipedia.org/wiki/Kernel_Patch_Protection > > Which unknown msrs are used by kernel patch protection? -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.