From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Bruce Rogers" Subject: Re: PAE issue (32-on-64 work) Date: Thu, 19 Oct 2006 07:18:13 -0600 Message-ID: <453726AF.092E.0048.1@novell.com> References: <45377204.76E4.0078.0@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: 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: Keir Fraser , xen-devel@lists.xensource.com, Jan Beulich List-Id: xen-devel@lists.xenproject.org NetWare is also a PAE guest, but doesn't put anything in the rest of the page, so zapping would be fine for NetWare. - Bruce >>> On 10/19/2006 at 6:56 AM, in message , Keir Fraser wrote: > On 19/10/06 11:39, "Jan Beulich" wrote: > >> Just now I found that there is a resulting issue for the 32on64 work I'm >> doing: Since none of the entries 4...511 of the PMD get initialized in > Linux, >> and since Xen nevertheless has to validate all 512 entries (in order to >> avoid making available translations that could be used during speculative >> execution), the validation has the potential to fail (and does in reality), >> resulting in the guest dying. The only option I presently see is to special >> case the compatibility guest in the l3 handling and (I really hate to do >> that) clear out the 518 supposedly unused entries (or at least clear >> their present bits), meaning that no guest may ever make clever >> assumptions and try to store some other data in the unused portion of >> the pgd page. > > Either copy the PGDs out into a shadow L3, as we do for PAE Xen today. Or, > as you say, zap the 508 unused entries. No guest uses them -- I'm pretty > sure Linux is the only PAE-capable guest (others are non-pae or 64-bit). > Storing other stuff in the page would be inconvenient anyway since it has to > be read-only. > > -- Keir > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel