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Date: Thu, 29 Jan 2015 20:33:38 -0500
From: Rik van Riel <riel@redhat.com>
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To: Dave Hansen <dave.hansen@linux.intel.com>, Oleg Nesterov <oleg@redhat.com>
CC: Suresh Siddha <sbsiddha@gmail.com>, Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Fenghua Yu <fenghua.yu@intel.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3]: x86, fpu: unlazy_fpu fixes/cleanups
References: <54C2A245.4010307@redhat.com> <20150129210723.GA31584@redhat.com> <54CAA357.1070108@linux.intel.com> <20150129213346.GA32511@redhat.com> <54CAA973.4050401@linux.intel.com> <20150129215638.GB1045@redhat.com> <54CAC190.30905@linux.intel.com>
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On 01/29/2015 06:26 PM, Dave Hansen wrote:
> On 01/29/2015 01:56 PM, Oleg Nesterov wrote:
>> --- x/arch/x86/kernel/traps.c +++ x/arch/x86/kernel/traps.c @@
>> -313,7 +313,7 @@ dotraplinkage void do_bounds(struct pt_r * It is
>> not directly accessible, though, so we need to * do an xsave and
>> then pull it out of the xsave buffer. */ -
>> fpu_save_init(&tsk->thread.fpu); +	unlazy_fpu(tsk); xsave_buf =
>> &(tsk->thread.fpu.state->xsave);
> ...
>> bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR);
> 
> Hmm, if the the thread was not using the FPU, and this fails to
> save anything in to the xsave_buf, what will bndcsr point to?

If the thread was not using the FPU, can we reach the
bound range exception?

I believe the MPX feature uses information in the xstate.

- -- 
All rights reversed
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