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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
To: Borislav Petkov <bp@suse.de>, Yu-cheng Yu <yu-cheng.yu@intel.com>
References: <cover.1462816638.git.yu-cheng.yu@intel.com>
 <c7710a66feae49c81347402baf86d18fe0718610.1462816638.git.yu-cheng.yu@intel.com>
 <20160510170130.GE28520@pd.tnic>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <5732159C.6030202@linux.intel.com>
Date: Tue, 10 May 2016 10:08:44 -0700
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On 05/10/2016 10:01 AM, Borislav Petkov wrote:
>> >  	pr_info("x86/fpu: Enabled xstate features 0x%llx, context size is %d bytes, using '%s' format.\n",
>> >  		xfeatures_mask,
>> > -		xstate_size,
>> > +		kernel_xstate_size,
>> >  		cpu_has_xsaves ? "compacted" : "standard");
> I think we should dump user_xstate_size in the compacted case since it
> is != kernel_xstate_size.

Why?  "kernel_xstate_size" is important to the kernel because it impacts
task_struct size.

But the kernel never actually stores "user_xstate_size" anywhere or
really ever even cares about it except when copying in/out of userspace.
 "user_xstate_size" is also entirely enumerable in userspace with a
single cpuid instruction.

It's nice to dump out interesting data in dmesg, but I'm curious why you
think it's interesting.