Re: [PATCH v3 9/9] x86/xsaves: Re-enable XSAVES

[Yu-cheng Yu]

On Tue, Mar 01, 2016 at 04:45:41PM -0800, Dave Hansen wrote:
> >>> +	WARN_ONCE((xfeatures_mask & XFEATURE_MASK_SUPERVISOR),
> >>> +		"x86/fpu: XSAVES supervisor states are not yet implemented.\n");
> >>> +
> >>>  	cr4_set_bits(X86_CR4_OSXSAVE);
> >>>  	xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask);
> >>>  }
> >>
> >> Let's also do a:
> >>
> >> 	xfeatures_mask &= ~XFEATURE_MASK_SUPERVISOR;
> >>
> >> Otherwise, we have a broken system at the moment.
> >>
> > Currently, if anyone sets any supervisor state in xfeatures_mask, the
> > kernel prints out the warning then goes into a protection fault.
> > That is a very strong indication to the user. Do we want to mute it? 
> 
> By "goes into a protection fault", do you mean that it doesn't boot?
> 
> I'd just rather we put the kernel in a known-safe configuration (masking
> supervisor state out of xfeatures_mask) rather than rely on the general
> protection fault continuing to be generated by whatever is generating it.
> 
Ok.

Yu-cheng