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Date: Mon, 2 May 2016 14:24:49 -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: <20160502212449.GA22532@test-lenovo>
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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!