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Re: kern/50332: AVX instructions don't work but OSXSAVE flag is set

On Tue, Oct 20, 2015 at 06:41:54PM +0200, Torbjörn Granlund wrote:
> David Laight <> writes:
>    No, there is no reason why you can't have a cpu (and os) that supports xsave
>    (etc) but doesn't support avx.
>    You have to look at the bitmap of supported extensions.
>    IIRC Only the x87 fpu registers are mandatory.
> Note that my updated test case tests both flags to make this a moot
> point.
>    However that probably isn't the issue here.
>    More likely is that something in xen should stop avx being used,
>    or xen needs to do something different from bare-metal to support avx.
> Please note that non-NetBSD guest systems have no problem.  Also, NetBSD
> with no Xen around works fine.
> That makes me suspect Xen is innocent and that NetBSD gets this wrong
> when run with Xen.
> My complaint is not that AVX does not work under Xen+NetBSD, but that it
> doesn't work in spite of that NetBSD sets OSXSAVE.

AFAIK NetBSD is not setting OSXSAVE. This comes from the cpuid instruction,
and I don't think the OS can change what cpuid repports.

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference

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