Messages in this thread | | | Subject | Re: [PATCH 17/21] x86/fpu: Use proper mask to replace full instruction mask | From | Dave Hansen <> | Date | Mon, 22 Jun 2020 08:02:44 -0700 |
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On 6/22/20 7:52 AM, Liang, Kan wrote: >>> --- a/arch/x86/kernel/fpu/xstate.c >>> +++ b/arch/x86/kernel/fpu/xstate.c >>> @@ -58,6 +58,7 @@ static short xsave_cpuid_features[] __initdata = { >>> * XSAVE buffer, both supervisor and user xstates. >>> */ >>> u64 xfeatures_mask_all __read_mostly; >>> +EXPORT_SYMBOL_GPL(xfeatures_mask_all); >> >> *groan*... >> >> AFAICT KVM doesn't actually use any of those functions, > > It seems KVM may eventually invoke copy_xregs_to_kernel() as below. > > kvm_save_current_fpu() > copy_fpregs_to_fpstate() > copy_xregs_to_kernel() > > I think we have to export the xfeatures_mask_all.
I'm wondering if we should just take these copy_*regs_to_*() functions and uninline them. Yeah, they are basically wrapping one instruction, but it might literally be the most heavyweight instruction in the whole ISA.
Or, maybe just make an out-of-line version for KVM to call?
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