linux-kernel - RE: xsaves support broken?

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Date:	Tue, 3 Mar 2015 00:34:02 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	"Hansen, Dave" <dave.hansen@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: RE: xsaves support broken?

> From: Hansen, Dave
> 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'.

QA did test conflict between MPX and xsaves long time before MPX went upstream. But seems the conflict happened again at some point...

> 
> > 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.

MPX and xsaves are supposed to work well on 4.0-rc1. If not, definitely the code is broken again somehow.

> 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.

We are supposed to handle this issue long time ago.

I can try to reproduce the issue with the config.

Thanks.

-Fenghua