linux-kernel - Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface

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Date:	Wed, 25 Jun 2014 14:43:13 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"Ren, Qiaowei" <qiaowei.ren@...el.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface

On 06/25/2014 02:04 PM, Andy Lutomirski wrote:
> On Tue, Jun 24, 2014 at 6:40 PM, Ren, Qiaowei <qiaowei.ren@...el.com> wrote:
>> Hmm, _install_special_mapping should completely prevent merging, even among MPX vmas.
>>
>> So, could you tell me how to set MPX specific ->name to the vma when it is created? Seems like that I could not find such interface.
> 
> You may need to add one.
> 
> I'd suggest posting a new thread to linux-mm describing what you need
> and asking how to do it.

I shared this with Qiaowei privately, but might as well repeat myself
here in case anyone wants to set me straight.

Most of the interfaces do to set vm_ops do it in file_operations ->mmap
op.  Nobody sets ->vm_ops on anonymous VMAs, so we're in uncharted
territory.

My suggestion: you can either plumb a new API down in to mmap_region()
to get the VMA or set ->vm_ops, or just call find_vma() after
mmap_region() or get_unmapped_area() and set it manually.  Just make
sure you still have mmap_sem held over the whole thing.

I think I prefer just setting ->vm_ops directly, even though it's a wee
bit of a hack to create something just to look it up a moment later.
Oh, well.

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