From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43347) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a748E-0003Lu-BU for qemu-devel@nongnu.org; Thu, 10 Dec 2015 11:31:51 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a748C-0008Md-FW for qemu-devel@nongnu.org; Thu, 10 Dec 2015 11:31:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54452) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a748C-0008MF-9r for qemu-devel@nongnu.org; Thu, 10 Dec 2015 11:31:48 -0500 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id F0B08C105B33 for ; Thu, 10 Dec 2015 16:31:47 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" Date: Thu, 10 Dec 2015 16:31:46 +0000 Message-Id: <1449765106-6528-1-git-send-email-dgilbert@redhat.com> Subject: [Qemu-devel] [PATCH] Fix xbzrle vs last_sent_block update List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: amit.shah@redhat.com, quintela@redhat.com From: "Dr. David Alan Gilbert" 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: 84e7b80a05c0c44b90533c6cd2f1db5c932ccf77 Signed-off-by: Dr. David Alan Gilbert --- migration/ram.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/migration/ram.c b/migration/ram.c index 1eb155a..0490f00 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -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; -- 2.5.0