From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 11 Nov 2014 18:27:37 +0000
Subject: Re: [PATCH v9 11/12] x86, mpx: cleanup unused bound tables
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To: Dave Hansen <dave.hansen@intel.com>
Cc: Qiaowei Ren <qiaowei.ren@intel.com>, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@linux-mips.org

On Thu, 6 Nov 2014, Dave Hansen wrote:
> Instead of all of these games with dropping and reacquiring mmap_sem and
> adding other locks, or deferring the work, why don't we just do a
> get_user_pages()?  Something along the lines of:
> 
> while (1) {
> 	ret = cmpxchg(addr)
> 	if (!ret)
> 		break;
> 	if (ret = -EFAULT)
> 		get_user_pages(addr);
> }
> 
> Does anybody see a problem with that?

You want to do that under mmap_sem write held, right? Not a problem per
se, except that you block normal faults for a possibly long time when
the page(s) need to be swapped in.

But yes, this might solve most of the issues at hand. Did not think
about GUP at all :(

Thanks,

	tglx