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Subject: Re: [PATCH v5 12/13] x86/xsaves: Fix fpstate_init() for XSAVES
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
References: <cover.1462816638.git.yu-cheng.yu@intel.com>
 <9c6c58a0a4a66568b8e887944d2426d59370ae05.1462816638.git.yu-cheng.yu@intel.com>
 <5731202B.2050805@linux.intel.com> <20160509235042.GB28442@test-lenovo>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, 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: <573124CC.8010505@linux.intel.com>
Date: Mon, 9 May 2016 17:01:16 -0700
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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...