From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.90_1) id 1os616-0004op-L5 for mharc-qemu-riscv@gnu.org; Mon, 07 Nov 2022 12:34:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1os613-0004iU-1R for qemu-riscv@nongnu.org; Mon, 07 Nov 2022 12:34:35 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1os611-0004q0-6M for qemu-riscv@nongnu.org; Mon, 07 Nov 2022 12:34:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667842470; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PEd3y9yQliodAttTxpeOjyz0tJTkJKzdnrRi7PdGEnc=; b=BUr6CdAK/YYOZr/WIO/uCcq2sY91a0c2oVLOKeFEAs9zOtBpYBX8VixQG4+c1hNF/pc4bp wA1GPYLuQKDPpMxvvaBZheYgncpnAtk5a/rystRwYtt54Qcprmp2ZnfUpqTvAK9DabsiAn f/10FUwauBLNGaeZuo1ZBugGPDeodWI= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-385-GkZrjLHqMEq2d8cqUYnffQ-1; Mon, 07 Nov 2022 12:34:26 -0500 X-MC-Unique: GkZrjLHqMEq2d8cqUYnffQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 554451C07596; Mon, 7 Nov 2022 17:34:26 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.58]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E41CD1121314; Mon, 7 Nov 2022 17:34:23 +0000 (UTC) Date: Mon, 7 Nov 2022 17:34:20 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Andrew Jones Cc: Alex =?utf-8?Q?Benn=C3=A9e?= , Sunil V L , Peter Maydell , Palmer Dabbelt , Alistair Francis , Bin Meng , Gerd Hoffmann , qemu-riscv@nongnu.org, qemu-devel@nongnu.org Subject: Re: [PATCH V2] hw/riscv: virt: Remove size restriction for pflash Message-ID: Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20221107130217.2243815-1-sunilvl@ventanamicro.com> <871qqehib4.fsf@linaro.org> <20221107173201.343hkqqugkzdzqcf@kamzik> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20221107173201.343hkqqugkzdzqcf@kamzik> User-Agent: Mutt/2.2.7 (2022-08-07) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-riscv@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 07 Nov 2022 17:34:35 -0000 On Mon, Nov 07, 2022 at 06:32:01PM +0100, Andrew Jones wrote: > On Mon, Nov 07, 2022 at 04:19:10PM +0000, Daniel P. Berrangé wrote: > > On Mon, Nov 07, 2022 at 03:50:44PM +0000, Alex Bennée wrote: > > > > > > Sunil V L writes: > > > > > > > On Mon, Nov 07, 2022 at 01:06:38PM +0000, Peter Maydell wrote: > > > >> On Mon, 7 Nov 2022 at 13:03, Sunil V L wrote: > > > >> > > > > >> > The pflash implementation currently assumes fixed size of the > > > >> > backend storage. Due to this, the backend storage file needs to be > > > >> > exactly of size 32M. Otherwise, there will be an error like below. > > > >> > > > > >> > "device requires 33554432 bytes, block backend provides 4194304 bytes" > > > >> > > > > >> > Fix this issue by using the actual size of the backing store. > > > >> > > > > >> > Signed-off-by: Sunil V L > > > >> > --- > > > >> > > > >> Do you really want the flash device size presented to the guest > > > >> to be variable depending on what the user passed as a block backend? > > > >> I don't think this is how we handle flash devices on other boards... > > > >> > > > > > > > > Hi Peter, > > > > > > > > x86 appears to support variable flash but arm doesn't. What is > > > > the reason for not supporting variable size flash in arm? > > > > > > If I recall from the last time we went around this is was the question > > > of what you should pad it with. > > > > Padding is a very good thing from the POV of upgrades. Firmware has shown > > a tendancy to change (grow) over time, and the size has an impact of the > > guest ABI/live migration state. > > > > To be able to live migrate, or save/restore to/from files, then the machine > > firmware size needs to be sufficient to cope with future size changes of > > the firmware. The best way to deal with this is to not use the firmware > > binaries' minimum compiled size, but instead to pad it upto a higher > > boundary. > > > > Enforcing such padding is a decent way to prevent users from inadvertantly > > painting themselves into a corner with a very specific firmware binary > > size at initial boot. > > Padding is a good idea, but too much causes other problems. When building > lightweight VMs which may pull the firmware image from a network, > AArch64 VMs require 64MB of mostly zeros to be transferred first, which > can become a substantial amount of the overall boot time[*]. Being able to > create images smaller than the total flash device size, but still add some > pad for later growth, seems like the happy-medium to shoot for. QEMU configures the firmware using -blockdev, so can use any file format that QEMU supports at the block layer. IOW, you can store the firmware in a qcow2 file and thus you will never fetch any of the padding zeros to be transferred. That said I'm not sure that libvirt supports anything other than a raw file today. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|