linux-kernel - Re: [PATCH 4/4] add ksm kernel shared memory driver.

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Date:	Thu, 16 Apr 2009 09:08:42 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org, avi@...hat.com,
	chrisw@...hat.com, mtosatti@...hat.com, hugh@...itas.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 4/4] add ksm kernel shared memory driver.

Andrea Arcangeli wrote:
> On Wed, Apr 15, 2009 at 05:43:03PM -0700, Jeremy Fitzhardinge wrote:
>   
>> Shouldn't that be kmap_atomic's job anyway?  Otherwise it would be hard to 
>>     
>
> No because those are full noops in no-highmem kernels. I commented in
> other email why I think it's safe thanks to the wrprotect + smp tlb
> flush of the userland PTE.
>   

I think Andrew's query was about data cache synchronization in 
architectures with virtually indexed d-cache.  On x86 it's a non-issue, 
but on architectures for which it is an issue, I assume kmap_atomic does 
any necessary cache flushes, as it does tlb flushes on x86 (which may be 
none at all, if no mapping actually happens).

    J

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