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SubjectRe: Finish removing MPX from arch/x86?
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On 10/4/22 19:34, Dave Hansen wrote:
> We zapped the userspace MPX ABIs and most of its supporting code in here:
>
> 45fc24e89b7c ("x86/mpx: remove MPX from arch/x86")
>
> But, the XSAVE enabling and KVM code were left in place. This let folks
> at least keep running guests with MPX.
>
> It's been a couple of years and I don't think I've had a single person
> opine about the loss of MPX. Intel also followed through and there's no
> MPX to be found on newer CPUs like my "Tiger Lake" 11th Gen Intel(R)
> Core(TM) i7-1165G7.
>
> Is it time to zap MPX from arch/x86/kvm/?

I agree that the likelihood of anybody complaining about MPX is low but
Jim is right that the timeline for removing it is unfortunately quite long.

Removing MPX from XFEATURE_MASK_USER_SUPPORTED is possible, though we
need to add a new XFEATURE_MASK_GUEST_SUPPORTED that includes MPX. I'll
take a look.

Also, it's worth noting that MPX lives in the sigcontext ABI because it
uses the non-compacted format. Because of that it is not possible to
remove the structs from include/asm/fpu/types.h, for example.

Paolo

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