From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: fsincos emulation on AMD CPUs Date: Thu, 15 Dec 2011 16:52:50 +0000 Message-ID: References: <4EEA020F0200007800068244@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4EEA020F0200007800068244@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: Paolo Bonzini , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 15/12/2011 13:19, "Jan Beulich" wrote: >>>> On 15.12.11 at 14:13, Keir Fraser wrote: >> On 15/12/2011 13:08, "Jan Beulich" wrote: >> >>>>>> On 15.12.11 at 13:33, Keir Fraser wrote: >>>> More detail: the full patch is ugly and hard to test all cases. And there's >>>> no practical scenario where we want to emulate FSINCOS on AMD -- we don't >>>> emulate realmode on AMD, FSINCOS on a shadowed page certainly indicates >>>> that >>>> we should unshadow the page, FSINCOS on MMIO is mad or malicious. >>> >>> Those latter two cases can't really happen, as fsincos has no memory >>> operand. >> >> Possibly if the instruction itself was in a recycled page-table page? Or in >> an MMIO page, or the malicious race that Paolo described --- definitely >> malicious either way. >> >> Anyhow the short answer is we never want to emulate it on AMD. :-) > > I just sent out the patch as quoted in the reply to Paolo, but you're > suggesting to be even more drastic and ignore the CPU family. If > you really want it done that way, I wonder whether we should bail on > AMD for *all* x87 operations not having memory operands. Your patch is fine. -- Keir > Jan >