linux-kernel - Re: [PATCH] s390: Add pmd

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Date:	Mon, 29 Oct 2012 12:05:19 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] s390: Add pmd_mknotpresent()


* Martin Schwidefsky <schwidefsky@...ibm.com> wrote:

> On Sun, 28 Oct 2012 14:10:14 +0100
> Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > There's a related problem on s390: other THP implementations 
> > have pmd_mknotpresent() while s390 not, resulting in:
> > 
> >   mm/huge_memory.c:1543:2: error: implicit declaration of function 'pmd_mknotpresent'
> > 
> > The (untested!) patch below adds the s390 version of this 
> > method.
> > 
> > Gerald, Martin, did I get the S390 details right?
> 
> This won't work I'm afraid. S390 uses invalid bits which need 
> to be set to make an entry not present. Just setting the 
> _SEGMENT_ENTRY_INV bit is not good enough either, there is 
> _HPAGE_TYPE_NONE to consider. The patch to fix this for 
> pmd_none & pmd_present just got added to the s390 tree on 
> kernel.org:
>
> https://git.kernel.org/?p=linux/kernel/git/s390/linux.git;a=shortlog;h=refs/heads/fixes
> 
> Now, if pmd_mknotpresent is supposed to make the entry invalid 
> so that pmd_present will return false the function needs to do 
> two things, 1) set the _SEGMENT_ENTRY_INV bit, and 2) clear 
> the _SEGMENT_ENTRY_RO bit.

Would be nice if you could send me your suggested 
pmd_mknotpresent().

(Writing it into the email would be enough, I can turn it into a 
patch - but a patch would be welcome as well.)

Thanks,

	Ingo
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