linux-kernel - Re: [PATCH v3 0/4] Intel MPX support

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Date:	Tue, 28 Jan 2014 10:26:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ren Qiaowei <qiaowei.ren@...el.com>, Ingo Molnar <mingo@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH v3 0/4] Intel MPX support

On 01/27/2014 11:01 PM, Ren Qiaowei wrote:
> 
> Yes. Though all non-MPX threads are slowed down, the whole process
> benefit from MPX.
> 
> Anyway, HPA suggest these syscalls, which use MMU notifier, should be
> not needed, we can do what they do in userspace runtime. What do you
> think about it? I guess that I should remove the third patch which adds
> new prctl() syscalls in next version of this patchset.
> 

The syscalls is one thing, managing the bounds map in kernel space is
another.

We could manage the bounds map entirely in user space in a signal
handler, but that has both ABI issues (#BR currently turns into SIGSEGV
which is commonly hooked by applications; we could switch to a different
signal but there aren't many unclaimed ones) and performance issues.

I would think it would be extremely unusual for an application to have
some MPX and some non-MPX threads, since they would share the same
address space and the non-MPX threads would mess up the bounds.

	-hpa

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