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Fix xbzrle vs last_sent_block update

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My fix (84e7b80a) replaced the last_sent_block update that I'd
removed earlier; however it was too aggressive in the xbzrle case.

save_xbzrle_page might return '0' to mean that the page didn't
need sending since it was the same as the last sent version;
in this case we can't update 'last_sent_block' since we didn't
actually send it.

Symptom: 'Illegal RAM offset 1018000' as we try and send a page
        to the wrong RAMBlock;  potentially that could be a data
        corruption if you were really unlucky.

Fixes: 84e7b80a05

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-id: 1449765106-6528-1-git-send-email-dgilbert@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Dr. David Alan Gilbert 2015-12-10 16:31:46 +00:00 committed by Peter Maydell
parent b969526adf
commit 3fd3c4b37c
1 changed files with 10 additions and 1 deletions
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11
migration/ram.c
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@ -716,6 +716,9 @@ static int save_zero_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset,
* ram_save_page: Send the given page to the stream
*
* Returns: Number of pages written.
* < 0 - error
* >=0 - Number of pages written - this might legally be 0
* if xbzrle noticed the page was the same.
*
* @f: QEMUFile where to send the data
* @block: block that contains the page we want to send
@ -1249,7 +1252,13 @@ static int ram_save_target_page(MigrationState *ms, QEMUFile *f,
if (unsentmap) {
clear_bit(dirty_ram_abs >> TARGET_PAGE_BITS, unsentmap);
}
last_sent_block = block;
/* Only update last_sent_block if a block was actually sent; xbzrle
* might have decided the page was identical so didn't bother writing
* to the stream.
*/
if (res > 0) {
last_sent_block = block;
}
}
return res;