linux-kernel - Re: mm: convert vma->vm

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Message-ID: <20110412203058.GC7806@n2100.arm.linux.org.uk>
Date:	Tue, 12 Apr 2011 21:30:58 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: mm: convert vma->vm_flags to 64bit

On Mon, Apr 11, 2011 at 11:33:58PM -0700, Andrew Morton wrote:
> How the heck did we end up using 32 flags??

Good question.

> > @@ -217,7 +217,7 @@ vivt_flush_cache_range(struct vm_area_struct *vma, unsigned long start, unsigned
> >  {
> >  	if (cpumask_test_cpu(smp_processor_id(), mm_cpumask(vma->vm_mm)))
> >  		__cpuc_flush_user_range(start & PAGE_MASK, PAGE_ALIGN(end),
> > -					vma->vm_flags);
> > +					(unsigned long)vma->vm_flags);
> >  }
> 
> I'm surprised this change (and similar) are needed?
> 
> Is it risky?  What happens if we add yet another vm_flags bit and
> __cpuc_flush_user_range() wants to use it?  I guess when that happens,
> __cpuc_flush_user_range() needs to be changed to take a ull.

The truncation is fine provided VM_EXEC is within the least significant
word.  If it isn't, then we'll blow up when the cache handling assembly
gets parsed by the assembler as the VM_EXEC value will overflow.
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