linux-kernel - Re: [PATCH 03/10] mm: Convert p[te|md]_numa users to p[te|md]_protnone

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Message-ID: <1417551190.27448.8.camel@kernel.crashing.org>
Date:	Wed, 03 Dec 2014 07:13:10 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LinuxPPC-dev <linuxppc-dev@...ts.ozlabs.org>,
	Hugh Dickins <hughd@...gle.com>, Dave Jones <davej@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 03/10] mm: Convert p[te|md]_numa users to
 p[te|md]_protnone_numa

On Tue, 2014-12-02 at 13:01 +0530, Aneesh Kumar K.V wrote:
> Benjamin Herrenschmidt <benh@...nel.crashing.org> writes:
> 
> > On Fri, 2014-11-21 at 13:57 +0000, Mel Gorman wrote:
> >> void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
> >>                 pte_t pte)
> >>  {
> >> -#ifdef CONFIG_DEBUG_VM
> >> -       WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);
> >> -#endif
> >> +       /*
> >> +        * When handling numa faults, we already have the pte marked
> >> +        * _PAGE_PRESENT, but we can be sure that it is not in hpte.
> >> +        * Hence we can use set_pte_at for them.
> >> +        */
> >> +       VM_WARN_ON((pte_val(*ptep) & (_PAGE_PRESENT | _PAGE_USER)) ==
> >> +               (_PAGE_PRESENT | _PAGE_USER));
> >> +
> >
> > His is that going to fare with set_pte_at() called for kernel pages ?
> >
> 
> Yes, we won't capture those errors now. But is there any other debug
> check i could use to capture the wrong usage of set_pte_at ?

Actually the above is fine, for some reason I mis-read the test as
blowing on kernel pages, it doesn't.

We probably do need to make sure however that protnone isn't used for
kernel pages.

Cheers,
Ben.

> -aneesh
> 
> --
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