From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56700) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a7Mlo-0002cQ-Rz for qemu-devel@nongnu.org; Fri, 11 Dec 2015 07:25:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a7Mll-0005rI-NU for qemu-devel@nongnu.org; Fri, 11 Dec 2015 07:25:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36674) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a7Mll-0005rE-Hf for qemu-devel@nongnu.org; Fri, 11 Dec 2015 07:25:53 -0500 From: Juan Quintela In-Reply-To: (Peter Maydell's message of "Thu, 10 Dec 2015 16:53:17 +0000") References: <1449765106-6528-1-git-send-email-dgilbert@redhat.com> Date: Fri, 11 Dec 2015 13:25:50 +0100 Message-ID: <87zixhkw8h.fsf@emacs.mitica> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH] Fix xbzrle vs last_sent_block update Reply-To: quintela@redhat.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Amit Shah , "Dr. David Alan Gilbert (git)" , QEMU Developers Peter Maydell wrote: D> On 10 December 2015 at 16:31, Dr. David Alan Gilbert (git) > wrote: >> 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; > > This sounds like we should probably put this into 2.5; I'm happy > to do so if it gets review by tomorrow afternoon and Juan/Amit > agree. Yeap, did the review by. Do you want a pull request, or just pick it directly?