* Dave Hansen <d...@sr71.net> wrote:
> On 05/20/2015 03:05 AM, Ingo Molnar wrote:
> >> >
> >> > This sees breakage unless either booted with 'noxsaves'
> >> > or if it has Fenghua's set from here applied:
> >> >
> >> >
> >> > http://lkml.kernel.org/r/1429678319-61356-1-git-send-email-fenghua...@intel.com
> >> >
> >> > This set is also available against 4.1-rc3 in git:
> >> >
> >> > git://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-mpx.git mpx-v22
>
> > Yeah, so as a first step, could you please test that the patch below solves
> > the crashes as well, without having to specify 'noxsaves' on the boot line?
>
> Yes, that does seem to make it happy in lieu of Fenghua's patches.
Great, thanks for testing it! I'll send it to Linus as part of x86/urgent.
> > + /*
> > + * Quirk: we don't yet handle the XSAVES* instructions
> > + * correctly, as we don't correctly convert between
> > + * standard and compacted format when interfacing
> > + * with user-space - so disable it for now.
> > + *
> > + * The difference is small: with recent CPUs the
> > + * compacted format is only marginally smaller than
> > + * the standard FPU state format.
> > + *
> > + * ( This is easy to backport while we are fixing
> > + * XSAVES* support. )
> > + */
> > + setup_clear_cpu_cap(X86_FEATURE_XSAVES);
> > }
>
> FWIW, I think it would be prudent to also clear X86_FEATURE_XSAVEC.
Ok, we can do that as well - but it's technically not needed to keep the kernel
from generating compact format FPU saves.
I'd also hope we can restore compact format handling soon-ish.
> All of the issues I am aware of are related to the compact format, not
> 'xsaves'
> itself (although 'xsaves' does *use* the compact format of course).
>
> The XSAVEC bit is the one that technically indicates the compact format
> support,
> although I don't think there is any actual use of it in the kernel at present.
Yeah.
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
