Re: [Xen-devel] [Patch 2/4] Refining Xsave/Xrestore support

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 28.10.10 at 09:55, Haitao Shan <maillists.shan@xxxxxxxxx> wrote:
> In my patch, if processor supports CR4.OSXSAVE, Xen will enable it and
> won't clear it as long as we are in ROOT mode.

Ah, okay. There's one problem with this, however - a pv domain the
kernel of which doesn't support xsave would still see CPUID report
the OSXSAVE bit set, and hence applications could be lead to
believe they can use the wider registers. I realize this also puts
under question our model of having the kernel look at CPUID's
OSXSAVE bit, but that could possibly be dealt with by having
pv_cpuid() (and perhaps xc_cpuid_pv_policy()) set the bit in case
Xen supports xsave.

Jan


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