linux-kernel - Re: x86/mm/pageattr: Code without effect?

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Message-ID: <5162D961.7030206@canonical.com>
Date:	Mon, 08 Apr 2013 16:51:13 +0200
From:	Stefan Bader <stefan.bader@...onical.com>
To:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Whitcroft <apw@...onical.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: x86/mm/pageattr: Code without effect?

On 08.04.2013 16:15, Borislav Petkov wrote:
> On Mon, Apr 08, 2013 at 03:10:00PM +0200, Stefan Bader wrote:
>>          * that we limited the number of possible pages already to
>>          * the number of pages in the large page.
>>          */
>>         if (address == (address & pmask) && cpa->numpages == (psize >>
>> PAGE_SHIFT)) {
>>                 /*
>>                  * The address is aligned and the number of pages
>>                  * covers the full page.
>>                  */
>>                 new_pte = pfn_pte(pte_pfn(old_pte), new_prot);
>>                                                      ^
>>
>> This one. The first patch changed
>>
>> -               new_pte = pfn_pte(pte_pfn(old_pte), canon_pgprot(new_prot));
>> +               new_pte = pfn_pte(pte_pfn(old_pte), new_prot);
>>
>> The fixup patch drops new_prot completely from being initialized and only works
>> on req_prot. Probably it would be best to also drop the definition of new_prot.
>> I think it then completely unused.
> 
> Actually, we do need and initialize new_prot at line 495:
> 
> 	pfn = pte_pfn(old_pte) + ((address & (psize - 1)) >> PAGE_SHIFT);
> 	cpa->pfn = pfn;
> 
> 	new_prot = static_protections(req_prot, address, pfn);		<---

You are right. Seems I missed that and a couble of other places. I can see them
now... Hm, Monday morning or just morning issue... So, yes, its new_prot is
initialized and is still needed, otherwise  the loop over the whole range would
be subtly different.
Sorry for the noise.

-Stefan

> 
> and we need it for the subsequent loop where we go over the 512 PTEs to
> decide whether to split or not.
> 
> So it is needed after all, AFAICT.
> 



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