linux-kernel - Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly

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Message-ID: <5727C75E.8000401@linux.intel.com>
Date:	Mon, 2 May 2016 14:32:14 -0700
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	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 v4 04/10] x86/xsaves: Introduce a new check that allows
 correct xstates copy from kernel to user directly

On 05/02/2016 02:24 PM, Yu-cheng Yu wrote:
> On Mon, May 02, 2016 at 02:18:17PM -0700, Yu-cheng Yu wrote:
>> > Before Linux gets into copy_fpstate_to_sigframe(),
>> > current->thread.fpu.fpstate_active must be true.
>> > For eagerfpu, fpregs_active() must also be true.
>> > For lazyfpu, once we try to do FSAVE/FXSAVE/XSAVE,
>> > fpregs_active() will become true as well.
>> > 
>> > We should have not based on boot_cpu_has(X86_FEATURE_XSAVES)
>> > at all. 
>> > 
>> > Why don't we make it simple and always copy_fpregs_to_signal_frame()?
>> > Or, only for the lazy case, i.e. !fpregs_active(), we do __copy_to_user().
> For (lazy && not XSAVES) actually!

I think we're off in the weeds here.

Please just send an updated patch for what you want to do here.