linux-kernel - Re: [PATCH v8 08/10] x86, mpx: add prctl commands PR_MPX_REGISTER, PR_MPX

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Date:	Fri, 12 Sep 2014 20:42:23 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave.hansen@...el.com>
cc:	Qiaowei Ren <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 08/10] x86, mpx: add prctl commands PR_MPX_REGISTER,
 PR_MPX_UNREGISTER

On Fri, 12 Sep 2014, Thomas Gleixner wrote:
> On Fri, 12 Sep 2014, Dave Hansen wrote:
> The proper solution to this problem is:
> 
>     do_bounds()
> 	bd_addr = get_bd_addr_from_xsave();
> 	bd_entry = bndstatus & ADDR_MASK:

Just for clarification. You CANNOT avoid the xsave here because it's
the only way to access BNDSTATUS according to the manual.

"The BNDCFGU and BNDSTATUS registers are accessible only with
 XSAVE/XRSTOR family of instructions"

So there is no point to cache BNDCFGU as you get it anyway when you
need to retrieve the invalid BD entry.

Thanks,

	tglx
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