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

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Message-ID: <20140128064202.GA20869@gmail.com>
Date:	Tue, 28 Jan 2014 07:42:02 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Ren Qiaowei <qiaowei.ren@...el.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	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


* Ren Qiaowei <qiaowei.ren@...el.com> wrote:

> >> MPX kernel code, namely this patchset, has mainly the 2 
> >> responsibilities: provide handlers for bounds faults (#BR), and 
> >> manage bounds memory.
> >
> > AFAICS the kernel side implementation causes no runtime overhead 
> > for non-MPX workloads, and also causes no runtime overhead for 
> > non-MPX hardware, right?
>
> Yes.

Actually, I think that's not entirely true.

For example if within the same mm there's a lot of non-MPX threads and 
an MPX thread, then the MMU notifier will be called for MMU operations 
of every non-MPX thread as well!

So MPX state of a thread will slow down all the other non-MPX threads 
as well.

The statement is only true for non-MPX tasks that have their separate 
mm's that does not have a single MPX thread.

Thanks,

	Ingo
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