On Tue, May 10, 2016 at 10:08:44AM -0700, Dave Hansen wrote:
> But the kernel never actually stores "user_xstate_size" anywhere or
> really ever even cares about it except when copying in/out of userspace.
Sounds like a reason enough to me.
> "user_xstate_size" is also entirely enumerable in userspace with a
> single cpuid instruction.
So is a lot of other stuff we're dumping in dmesg.
> It's nice to dump out interesting data in dmesg, but I'm curious why you
> think it's interesting.
I think it would be interesting to know what the kernel's idea
is of user_xstate_size. I know, I know, one can follow the code
and figure out what it is but one can say the same about a lot of
other "interesting" data dumped in dmesg. And I'd like to know what
fpu__init_system_xstate_size_legacy() decided. And so I know how many
data is shuffled to/from userspace.
And btw, this message needs more "humanization":
[ 0.000000] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256
That doesn't tell me anything.
Oh and it can be read out from CPUID too.
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
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