Commit 3fd3c4b3 authored Dec 10, 2015 by Dr. David Alan Gilbert Committed by Peter Maydell Dec 11, 2015

Fix xbzrle vs last_sent_block update



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: 84e7b80a

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>

parent b969526a

migration/ram.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -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
		@@ -1249,8 +1252,14 @@ static int ram_save_target_page(MigrationState ms, QEMUFile f,
		if (unsentmap) {
		clear_bit(dirty_ram_abs >> TARGET_PAGE_BITS, unsentmap);
		}
		/* 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;
		}