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Date: Mon, 2 May 2016 09:34:10 -0700
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@suse.de>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>
Subject: Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows
 correct xstates copy from kernel to user directly
Message-ID: <20160502163410.GA21734@test-lenovo>
References: <cover.1457038929.git.yu-cheng.yu@intel.com>
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On Mon, May 02, 2016 at 09:06:41AM -0700, Dave Hansen wrote:
> On 05/02/2016 08:57 AM, Yu-cheng Yu wrote:
> > On Fri, Apr 29, 2016 at 05:36:48PM -0700, Dave Hansen wrote:
> >> If may_copy_fpregs_to_sigframe() were called from a slightly different
> >> context, or if we change the call-site, what breaks?
> >>
> >> In other words. if we can still "may_copy_fpregs_to_sigframe()" no
> >> matter the state of fpu.fpstate_active, then I don't think we should be
> >> checking it in may_copy_fpregs_to_sigframe().
> > 
> > Do you mean, don't check fpu.fpstate_active here?
> 
> Not really.  I'm asking *why* the check is there.

If (fpu.fpstate_active == 0), then the task does not use FPU; we don't
want to save these registers, right?