Messages in this thread | | | Subject | Re: [PATCH v3 9/9] x86/xsaves: Re-enable XSAVES | From | Dave Hansen <> | Date | Tue, 1 Mar 2016 15:56:12 -0800 |
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On 02/29/2016 09:42 AM, Yu-cheng Yu wrote: > /* > - * 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. ) > + * Most recent CPUs supporting XSAVES can run 64-bit mode. > + * Enable XSAVES for 64-bit. > */ > - setup_clear_cpu_cap(X86_FEATURE_XSAVES); > + if (!config_enabled(CONFIG_X86_64)) > + setup_clear_cpu_cap(X86_FEATURE_XSAVES); > }
I think we need a much better explanation of this for posterity. Why are we not supporting this now, and what would someone have to do in the future in order to enable it?
> /* > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > index 2e80d6f..cb2a484 100644 > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -204,6 +204,14 @@ void fpu__init_cpu_xstate(void) > if (!cpu_has_xsave || !xfeatures_mask) > return; > > + /* > + * Make it clear that XSAVES supervisor states are not yet > + * implemented should anyone expect it to work by changing > + * bits in XFEATURE_MASK_* macros and XCR0. > + */ > + 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.
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