linux-kernel - Re: [PATCH 0/4] [RFC][v4] Workaround for Xeon Phi PTE A/D bits erratum

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Message-ID: <829f2f03-8492-841d-869f-7fd7add9cb27@suse.cz>
Date:	Wed, 13 Jul 2016 14:10:07 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, linux-mm@...ck.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, bp@...en8.de, ak@...ux.intel.com,
	mhocko@...e.com
Subject: Re: [PATCH 0/4] [RFC][v4] Workaround for Xeon Phi PTE A/D bits
 erratum

On 07/13/2016 01:37 PM, Vlastimil Babka wrote:
>> > With the errata, don't you have a situation where a processor in the second
>> > category will write and set D despite P having been cleared (due to the
>> > race) and thus causing us to miss the transfer of that D to the struct
>> > page and essentially completely miss that the physical page is dirty ?
> Seems to me like this is indeed possible, but...

Nevermind, I have read the v3 thread now, where Dave says [1] that 
setting the D bit due to the erratum doesn't mean that the page is 
really actually written to (it's not). So there shouldn't be any true 
dirty bit to leave behind.

[1] http://marc.info/?l=linux-mm&m=146738965614826&w=2