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Subject: Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID
To: Kyle Huey <me@kylehuey.com>
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From: "H. Peter Anvin" <hpa@zytor.com>
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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