From: Sachin Sant <sachinp@in•ibm.com>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: linuxppc-dev@ozlabs•org, Paul Mackerras <paulus@samba•org>
Subject: Re: [PATCH] powerpc/mm: Fix potential access to freed pages when using hugetlbfs
Date: Wed, 17 Jun 2009 14:48:34 +0530 [thread overview]
Message-ID: <4A38B4EA.20507@in.ibm.com> (raw)
In-Reply-To: <20090616025419.A5581DDD1B@ozlabs.org>
Benjamin Herrenschmidt wrote:
> When using 64k page sizes, our PTE pages are split in two halves,
> the second half containing the "extension" used to keep track of
> individual 4k pages when not using HW 64k pages.
>
> However, our page tables used for hugetlb have a slightly different
> format and don't carry that "second half".
>
> Our code that batched PTEs to be invalidated unconditionally reads
> the "second half" (to put it into the batch), which means that when
> called to invalidate hugetlb PTEs, it will access unrelated memory.
>
> It breaks when CONFIG_DEBUG_PAGEALLOC is enabled.
>
> This fixes it by only accessing the second half when the _PAGE_COMBO
> bit is set in the first half, which indicates that we are dealing with
> a "combo" page which represents 16x4k subpages. Anything else shouldn't
> have this bit set and thus not require loading from the second half.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Thanks for the patch. The machine survived after two days of
testing with hugetlbfs tests.
Regards
-Sachin
--
---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
---------------------------------
next prev parent reply other threads:[~2009-06-17 9:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-16 2:53 [PATCH] powerpc/mm: Fix potential access to freed pages when using hugetlbfs Benjamin Herrenschmidt
2009-06-17 9:18 ` Sachin Sant [this message]
2009-06-17 10:11 ` Benjamin Herrenschmidt
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