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Date: Wed, 08 Jul 2009 09:29:22 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] qcow2: Fix L1 table memory allocation
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To: malc <av1474@comtv.ru>
Cc: Avi Kivity <avi@redhat.com>, qemu-devel@nongnu.org

malc schrieb:
> On Tue, 7 Jul 2009, Avi Kivity wrote:
> 
>> On 07/07/2009 07:09 PM, Kevin Wolf wrote:
>>> Contrary to what one could expect, the size of L1 tables is not cluster
>>> aligned. So as we're writing whole sectors now instead of single entries,
>>> we need to ensure that the L1 table in memory is large enough; otherwise
>>> write would access memory after the end of the L1 table.
>>>
>>>
>>>       new_l1_size2 = sizeof(uint64_t) * new_l1_size;
>>> -    new_l1_table = qemu_mallocz(new_l1_size2);
>>> +    new_l1_table = qemu_mallocz(align_offset(new_l1_size2, 512));
>>>       memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
>>>    
>> Unrelated note: using qemu_memalign() here would reduce the copying for
>> cache=none.
>>
> 
> Another unrelated note, qemu_memalign(and by extension qemu_vmalloc)
> is NULL happy. And FWIW 487414f1cbd638beb0227c7da71fe7b8a821e155
> removed NULL checks for qemu_memalgn and after that new code was added
> that doesn't check for NULLs either (for instance e3f4e2a4 which has
> bitten me).

Good to know that there still is an alternative that isn't broken.
Another good reason to switch to qemu_memalign.

Kevin