Date: Tue, 8 Dec 2015 19:48:19 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave@sr71.net>
cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
        dave.hansen@linux.intel.com
Subject: Re: [PATCH 30/34] x86, fpu: allow setting of XSAVE state
In-Reply-To: <20151204011506.7A3C77FA@viggo.jf.intel.com>
Message-ID: <alpine.DEB.2.11.1512081948020.3595@nanos>
References: <20151204011424.8A36E365@viggo.jf.intel.com> <20151204011506.7A3C77FA@viggo.jf.intel.com>
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On Thu, 3 Dec 2015, Dave Hansen wrote:

> 
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> We want to modify the Protection Key rights inside the kernel, so
> we need to change PKRU's contents.  But, if we do a plain
> 'wrpkru', when we return to userspace we might do an XRSTOR and
> wipe out the kernel's 'wrpkru'.  So, we need to go after PKRU in
> the xsave buffer.
> 
> We do this by:
> 1. Ensuring that we have the XSAVE registers (fpregs) in the
>    kernel FPU buffer (fpstate)
> 2. Looking up the location of a given state in the buffer
> 3. Filling in the stat
> 4. Ensuring that the hardware knows that state is present there
>    (basically that the 'init optimization' is not in place).
> 5. Copying the newly-modified state back to the registers if
>    necessary.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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