From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: Re: Xen's use of PAT and PV guests Date: Wed, 31 Mar 2010 09:26:19 +0100 Message-ID: <4BB3234B0200007800038153@vpn.id2.novell.com> References: <4BB1476D.4060209@goop.org> <20100330165713.GA7439@phenom.dumpdata.com> <4BB2463A.9090401@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <4BB2463A.9090401@goop.org> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jeremy Fitzhardinge , Konrad Rzeszutek Wilk Cc: Xen-devel , Keir Fraser List-Id: xen-devel@lists.xenproject.org >>> Jeremy Fitzhardinge 30.03.10 20:43 >>> >On 03/30/2010 09:57 AM, Konrad Rzeszutek Wilk wrote: >> How does this work on pages shared across domains? Say Guest A makes = the >> page WC,Dom0 makes it WB and Xen puts it in WC, and Dom0 reads does a >> Write/Read/Write, but in actuallity it is a Read/Write/Write. Or is >> there no danger there since the grant table pages have UC set on them? >> =20 > >Not sure. That would invoke undefined behaviour, I'd assume. Does = Xen=20 >keep track of memory type aliases? Grant pages don't have to be UC do=20 >they? Pages between front and backends don't need to be (and shouldn't=20= >be) UC. Granted pages are RAM pages, and hence should always be WB everywhere. As to Xen's memory type handling - iirc the most recent memory type used in a page table entry determines what Xen uses in its 1:1 mapping, but I don't think global consistency is being enforced. Jan