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Re: [Xen-devel] [PATCH v3] Sanity check xsave area when migrating or restoring from older Xen verions

On Tue, 21 Oct 2014 16:29:58 +0100
Jan Beulich <JBeulich@xxxxxxxx> wrote:

> >>> On 21.10.14 at 17:15, <dkoch@xxxxxxxxxxx> wrote:
> > The one anomaly I've wondered about is the point of
> > ctxt->xfeature_mask; we save it but never use it (outside of a print
> > statement) on restore. Do we want to compare it against the global
> > xfeature_mask for sanity (print a warning on mismatch) or just ignore
> > it. I wouldn't suggest removing it as it would cause another
> > compatibility issue with migration.
> This was discussed before, and you could also turn to the commit
> which eliminated its use to understand why (e2e45c5628
> "x86/xsave: remove xfeat_mask checking from validate_xstate()").
> And yes, eliminating the _field_ is not an option.

Thanks for the reference.

Looking at validate_xstate(), I've concluded that the check against the
xfeature_mask is a superset of the check against xcr0_accum as the latter
is a subset of the former and can only be smaller. Will remove the
xfeature_mask size test.

> Jan


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