Re: [Qemu-devel] [PATCH] os: don't corrupt pre-existing memory-backend data with prealloc

[Stefan Hajnoczi]

On Fri, Feb 24, 2017 at 05:27:14PM +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>
> ---
> 
> NB, I have not tested performance of this, so no idea if this
> makes it better/worse/no-change. Would appreciate if Jitendra
> could repeat tests to see if it impacts scalability at all.
> 
>  util/oslib-posix.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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