From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave McCracken Subject: Re: Re: [PATCH 2/2] Linux support for hugepages as a Xen PV guest Date: Wed, 15 Oct 2008 12:01:06 -0500 Message-ID: <200810151201.06367.dcm@mccr.org> References: <200810101006.44389.dcm@mccr.org> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200810101006.44389.dcm@mccr.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: xen-devel@lists.xensource.com Cc: Keir Fraser List-Id: xen-devel@lists.xenproject.org On Friday 10 October 2008, Dave McCracken wrote: > On Friday 10 October 2008, Keir Fraser wrote: > > hugetlbfs should only be enabled at runtime if supported by the > > hypervisor. Perhaps we can enable the PSE CPUID flag if the hypervisor > > supports superpages? > > I'll look into it. Opening the cover to this exposed some very interesting things on the Linux side. For starters, Xen currently does remove PSE from the CPUID it returns to the guest. I'll add some code to allow PSE when hugepages are enabled. Second, in Linux for the x86_64 architecture the macro to check for PSE is hard-wired to always be true. Third, hugepages in Linux makes no check whatsoever for the presence or absence of PSE. It assumes it's there. I'll look into the simplest way to make the various Linux parts obey the PSE flag properly. Dave McCracken Oracle Corp. This is all for the Linux-xen-2.6.18 tree on xensource.