linux-kernel - Re: [PATCH v5 12/13] x86/xsaves: Fix fpstate

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Date:	Mon, 9 May 2016 17:01:16 -0700
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:	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>,
	Borislav Petkov <bp@...e.de>,
	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 12/13] x86/xsaves: Fix fpstate_init() for XSAVES

On 05/09/2016 04:50 PM, Yu-cheng Yu wrote:
>> > 
>> > Oh, and if you decided to do this for some reason, please have mercy and
>> > go make a macro for 1<<63.
>> > 
>> > Also, I don't think the kernel ever checks for this bit.  So are we
>> > really calling XRSTORS on otherwise uninitialized xsave buffers?
> Right now if we do fpstate_init(), without this patch, it will 
> trigger a warning from copy_kernel_to_fxregs() when the task is
> scheduled.

Please include this in the patch description.  It's a pretty important
piece of justification.  Did you mean "copy_kernel_to_xregs()" without
the "f"?

I think we should probably also have an _explicit_ FPU_WARN_ON() in the
XRSTORS path for this.  *Both* the booting and regular ones, btw...