linux-kernel - Re: Arch specific mmap attributes (Was: mprotect pgprot handling weirdness)

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Date:	Tue, 06 Apr 2010 17:30:44 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org
Subject: Re: Arch specific mmap attributes (Was: mprotect pgprot handling
 weirdness)

On Tue, 2010-04-06 at 15:24 +0900, KOSAKI Motohiro wrote:

> I guess you haven't catch my intention. I didn't say we have to remove 
> PROT_SAO and VM_SAO.
> I mean mmap(PROT_SAO) is ok, it's only append new flag, not change exiting
> flags meanings. I'm only against mprotect(PROT_NONE) turn off PROT_SAO
> implicitely.
> 
> IOW I recommend we use three syscall
> 	mmap()		create new mappings
> 	mprotect()	change a protection of mapping (as a name)
> 	mattribute(): (or similar name)
> 			change an attribute of mapping (e.g. PROT_SAO or
> 			another arch specific flags)
> 
> I'm not against changing mm/protect.c for PROT_SAO.

Ok, I see. No biggie. The main deal remains how we want to do that
inside the kernel :-) I think the less horrible options here are
to either extend vm_flags to always be 64-bit, or add a separate
vm_map_attributes flag, and add the necessary bits and pieces to
prevent merge accross different attribute vma's.

The more I try to hack it into vm_page_prot, the more I hate that
option.

Cheers
Ben.


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