Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID

From: H. Peter Anvin
Date: Tue Mar 14 2017 - 16:10:09 EST


On 03/14/17 12:08, Kyle Huey wrote:
>
> That's largely what we ended up doing. See
> https://lkml.org/lkml/2017/2/14/80 and the latest version of this
> patch, https://lkml.org/lkml/2017/3/11/197.
>

Yes, as I said, my mistake.

I would still like to see an early-out when none of these flags are set
(I just discussed this with tglx on IRC):

if (likely(!((tifp|tifn) &
(_TIF_BLOCKSTEP|_TIF_NOTSC|_TIF_IO_BITMAP|
_TIF_NOCPUID|_TIF_USER_RETURN_NOTIFY))))
return;

The USER_RETURN_NOTIFY could really use some sanity: it is a notifier
chain with a single in-kernel user, which is KVM on x86 only, but we
most likely will need to propagate the flag even if it ends up getting
specialized.

-hpa