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Re: [Qemu-devel] [PATCH v3] os: don't corrupt pre-existing memory-backen

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v3] os: don't corrupt pre-existing memory-backend data with prealloc
Date: Fri, 10 Mar 2017 09:34:29 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 10/03/2017 05:30, Stefan Hajnoczi wrote:
> On Fri, Mar 03, 2017 at 11:32:55AM +0000, Daniel P. Berrange wrote:
>> When using a memory-backend object with prealloc turned on, QEMU
>> will memset() the first byte in every memory page to zero. While
>> this might have been acceptable for memory backends associated
>> with RAM, this corrupts application data for NVDIMMs.
>> Instead of setting every page to zero, read the current byte
>> value and then just write that same value back, so we are not
>> corrupting the original data. Directly write the value instead
>> of memset()ing it, since there's no benefit to memset for a
>> single byte write.
>> Signed-off-by: Daniel P. Berrange <address@hidden>
>> ---
>> Changed in v3:
>>  - Mark the target of the write as volatile, instead of the intermedia
>>    variable (Andrea)
>>  util/oslib-posix.c | 15 ++++++++++++++-
>>  1 file changed, 14 insertions(+), 1 deletion(-)
> There are no official maintainers for this source file.  I want to make
> sure this patch goes into QEMU 2.9, so...
> Thanks, applied to my block tree:
> https://github.com/stefanha/qemu/commits/block

Yeah, I was leaving it to you because it's related to NVDIMM.  Thanks,


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