linux-kernel - RE: xsaves support broken?

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Date:	Tue, 3 Mar 2015 00:09:25 +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
> Sent: Monday, March 02, 2015 4:00 PM
> 
> Hi Fenghua,
> 
> I was testing some new MPX code, and realized that MPX had stopped
> working completely.  The prctl() failed to turn it on, which I tracked down to a
> 0 in "BNDCSR" where we expected to see an enable bit.
> 
> I realized that I had managed to remove the "noxsaves" boot option from my
> kernel.  Re-adding "noxsaves" made MPX work again, and the BNDCSR
> contents were properly passed in to the kernel.
> 
> Is it possible that  "xsaves" use inside the kernel is simply broken?
> 
> Config is here:
> 
> 	http://sr71.net/~dave/intel/config-20150302

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.

What changes in your new MPX code?

Thanks.

-Fenghua