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

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Oct 20, 2015 at 06:41:54PM +0200, Torbjörn Granlund wrote:
> David Laight <david%l8s.co.uk@localhost> 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 <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--