linux-kernel - Re: [PATCH v5 02/13] x86/xsaves: Rename xstate_size to kernel_xstate_size to explicitly distinguish xstate size in kernel from user space

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Date:	Tue, 10 May 2016 10:31:38 -0700
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Yu-cheng Yu <yu-cheng.yu@...el.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v5 02/13] x86/xsaves: Rename xstate_size to
 kernel_xstate_size to explicitly distinguish xstate size in kernel from user
 space

On 05/10/2016 10:26 AM, Borislav Petkov wrote:
>> > It's nice to dump out interesting data in dmesg, but I'm curious why you
>> > think it's interesting.
> I think it would be interesting to know what the kernel's idea
> is of user_xstate_size. I know, I know, one can follow the code
> and figure out what it is but one can say the same about a lot of
> other "interesting" data dumped in dmesg. And I'd like to know what
> fpu__init_system_xstate_size_legacy() decided. And so I know how many
> data is shuffled to/from userspace.
> 
> And btw, this message needs more "humanization":
> 
> [    0.000000] x86/fpu: xstate_offset[2]:  576, xstate_sizes[2]:  256
> 
> That doesn't tell me anything.
> 
> Oh and it can be read out from CPUID too.

That all sounds like great stuff to do in a follow-on patchset after
this XSAVES stuff.