Re: Word-at-a-time dcache name accesses (was Re: .. anybody knowof any filesystems that depend on the exact VFS 'namehash' implementation?)

[H. Peter Anvin]

On 03/02/2012 05:11 PM, Linus Torvalds wrote:
> On Fri, Mar 2, 2012 at 5:02 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>>
>> Note that does mean we need a guard page after each and every
>> discontiguous RAM range, not just the last one.  Raising that issue
>> since we have had serious bugs in that area in the past.
> 
> Are you sure? I didn't think we even *mapped* things at that granularity.
> 
> We only really need a guard page at the end of an actual end-of-ram
> where we no longer have page tables and/or could hit device space.
> 

Yes of course.  Note that I'm currently pushing for mapping only RAM
regions; we have a lot of bugs and workarounds related to mapping too
much, and the answer to fixing that should be pretty obvious.

> For robustness and actual deployment, I do think that yes, we do want
> to make it an explicit rule.

Definitely.  Ideally those pages should be zeroed and mapped readonly.

	-hpa



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