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Subject: Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows
 correct xstates copy from kernel to user directly
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
References: <5723BF63.2000100@linux.intel.com>
 <20160429224338.GA15757@test-lenovo> <5723FE20.7000906@linux.intel.com>
 <20160502155734.GA21577@test-lenovo> <57277B11.9080802@linux.intel.com>
 <20160502163410.GA21734@test-lenovo> <572783C3.8040907@linux.intel.com>
 <20160502171936.GA22224@test-lenovo> <57278F56.6050600@linux.intel.com>
 <20160502211817.GA22492@test-lenovo> <20160502212449.GA22532@test-lenovo>
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>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <5727C75E.8000401@linux.intel.com>
Date: Mon, 2 May 2016 14:32:14 -0700
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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.