From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4199AC433FE for ; Mon, 7 Nov 2022 17:35:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1os617-0004sA-IR; Mon, 07 Nov 2022 12:34:37 -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 1os612-0004iL-Od for qemu-devel@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 1os610-0004pW-94 for qemu-devel@nongnu.org; Mon, 07 Nov 2022 12:34:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667842468; 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=ElLgPJ55+/+4fbps0gADs531lGX86o4bFOEz4KqfPWDXfL6+6bc4k0w57nB7W0IM8ImLHw TIA0MftqMStgWtunX+1Xdi3TCCWYy+n6UkyXAgrcScMsbIxOEolB3/rd1rBHmxKsJZ57+d 9tjsN5RB4TZhQqnB17mioHZJfHT4cFM= 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: 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=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org 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 :|