Re: [Xen-devel] [PATCH] linux: fix grant table bug

To:	Michael Abd-El-Malek <mabdelmalek@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] linux: fix grant table bug
From:	Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date:	Mon, 31 Mar 2008 10:53:04 +0100
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On 31/3/08 04:42, "Michael Abd-El-Malek" <mabdelmalek@xxxxxxx> wrote:

> A PV OS has two grant table data structures: the grant table itself and a free
> list.  The free list is composed of an array of pages, which grow dynamically
> as 
> the guest OS requires more grants.  While the grant table contains 8-byte
> entries, the free list contains 4-byte entries.  So we have half as many pages
> in the free list than in the grant table.
> 
> There was a bug in the free list allocation code. The free list was indexed as
> if it was the same size as the grant table.  But it's only half as large.  So
> memory got corrupted, and I was seeing crashes in the slab allocator later on.

Nice catch. That code is a bit confusing!

 -- Keir



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