Re: [Xen-devel] Re: [PATCH 2/2] Linux support for hugepages as a Xen PV guest

[Dave McCracken <dcm@xxxxxxxx>]

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.

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