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Re: [Xen-devel] [PATCH] x86/xsave: Expose xsave_cntxt_size to avoid reloading xcr0

>>> On 04.06.14 at 13:56, <andrew.cooper3@xxxxxxxxxx> wrote:
> xstate_ctxt_size(xfeature_mask) is runtime constant after boot.  There is no
> need to reload xcr0 twice for this basic bounds check.

Honestly I'm not in favor of exposing this variable for a not
performance critical code path. If we really care about saving a few
cycles here, how about having xstate_ctxt_size() check its argument
against xfeature_mask and return xsave_cntxt_size if equal?
Admittedly that'll need some extra care for the uses of the function
in xstate_init(), but it's not horribly difficult to make the current
function an internal one, and the global one be a wrapper with that
check done first.


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