From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43685) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XqzjZ-0006rG-O5 for qemu-devel@nongnu.org; Wed, 19 Nov 2014 02:31:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XqzjT-0008Ol-J4 for qemu-devel@nongnu.org; Wed, 19 Nov 2014 02:31:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38857) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XqzjT-0008Oh-Bz for qemu-devel@nongnu.org; Wed, 19 Nov 2014 02:31:19 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id sAJ7VIxN002828 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 19 Nov 2014 02:31:18 -0500 Date: Wed, 19 Nov 2014 13:01:14 +0530 From: Amit Shah Message-ID: <20141119073114.GF9190@grmbl.mre> References: <1416254843-16859-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1416254843-16859-1-git-send-email-mst@redhat.com> Subject: Re: [Qemu-devel] [PATCH 0/5] pc: make ROMs resizeable List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: pbonzini@redhat.com, Juan Quintela , qemu-devel@nongnu.org, dgilbert@redhat.com On (Mon) 17 Nov 2014 [22:08:46], Michael S. Tsirkin wrote: > At the moment we migrate ROMs which reside in fw cfg, which allows > changing ROM code at will, and supports migrating largish blocks early, > with good performance. > However, we are running into a problem: changing size breaks > migration every time. > This already requires somewhat messy compatibility support in > acpi generation code, and it looks like there'll be more to come. > > Rather than try to guess the correct size once and for all, > this patchset tries to make code future-proof, by > adding support for resizeable ram blocks. > > A (possibly very high) amount of space in ram_addr_t space is reserved > for each block, but never allocated. > If incoming block size differs from current size, block is > reallocated. FW CFG is also notified and updated accordingly. > > To simplify things, I didn't add support for resizing > actual RAM: device RAM such as fw cfg ROMs are never mapped > into guests directly, so instead I added an API to > flag device RAM explicitly, and manage them using > simple alloc/free/realloc > > Considering this promises to rid us of worries about ROM size considerations > once and for all, I thinking about pushing this as a "kind of bugfix" before > 2.2, so we don't need to maintain more band-aids in 2.3 and on. I'd rather wait for 2.3; we've done this for a couple of releases already, so what's one more. And we're at rc2 already.. > Note: migration stream is unaffected by these patches. > This makes it possible to enable this functionality > unconditionally, for all machine types. > > In the future, this might be handy for other things, > such as changing kernels loaded on command line > across migrations. I think that'll be too risky; unless we do S4 before / after migration to ensure the kernel realises things might be changing beneath its feet. Amit