linux-kernel - Re: xsaves support broken?

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Date:	Mon, 02 Mar 2015 16:24:12 -0800
From:	Dave Hansen <dave.hansen@...el.com>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: xsaves support broken?

On 03/02/2015 04:09 PM, Yu, Fenghua wrote:
> Xsaves has been tested by QA since 3.17 with or without MPX. I'm not
> aware of reported issues.
> 
> But MPX is the only code to call the get_xsave_addr kernel API.
> Though it has been tested before on upstream MPX code.

Has it?  I'm fairly sure I've never explicitly tested it.  I'm also
doubting now that I've *ever* seen it work without booting with 'noxsaves'.

> What changes in your new MPX code?

I just discovered it when adding a new feature.  I actually backed out
all of my changes before reporting this issue.  I'm running a completely
untouched 4.0-rc1 kernel with the config I attached a moment ago.

If I boot with 'noxsaves', MPX works fine.  If I boot without it, the
kernel never sees the values that userspace sets in the "bndcsr" register.

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