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Thu, 30 Jul 2020 04:39:07 +0000 (UTC) Subject: Re: [PATCH for-5.2 0/6] Continue booting in case the first device is not bootable To: Viktor Mihajlovski , qemu-devel@nongnu.org References: <20200728183734.7838-1-thuth@redhat.com> <5c860673-9c0c-79fe-2804-4864856257f5@linux.ibm.com> From: Thomas Huth Openpgp: preference=signencrypt Message-ID: Date: Thu, 30 Jul 2020 06:39:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <5c860673-9c0c-79fe-2804-4864856257f5@linux.ibm.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/29 22:19:00 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-1, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 29/07/2020 13.42, Viktor Mihajlovski wrote: > > > On 7/28/20 8:37 PM, Thomas Huth wrote: >> If the user did not specify a "bootindex" property, the s390-ccw bios >> tries to find a bootable device on its own. Unfortunately, it alwasy >> stops at the very first device that it can find, no matter whether it's >> bootable or not. That causes some weird behavior, for example while >> >>   qemu-system-s390x -hda bootable.qcow2 >> >> boots perfectly fine, the bios refuses to work if you just specify >> a virtio-scsi controller in front of it: >> >>   qemu-system-s390x -device virtio-scsi -hda bootable.qcow2 >> >> Since this is quite uncomfortable and confusing for the users, and >> all major firmwares on other architectures correctly boot in such >> cases, too, let's also try to teach the s390-ccw bios how to boot >> in such cases. >> >> For this, we have to get rid of the various panic()s and IPL_assert() >> statements at the "low-level" function and let the main code handle >> the decision instead whether a boot from a device should fail or not, >> so that the main code can continue searching in case it wants to. >> > > Looking at it from an architectural perspective: If an IPL Information > Block specifying the boot device has been set and can be retrieved using > Diagnose 308 it has to be respected, even if the device doesn't contain > a bootable program. The boot has to fail in this case. > > I had not the bandwidth to follow all code paths, but I gather that this > is still the case with the series. Right. Just to be sure, I just double-checked with: ... -device virtio-blk,drive=baddrive,bootindex=1 \ -device virtio-blk,drive=gooddrive and indeed, the s390-ccw bios only checks the "baddrive" here and refuses to boot. > So one can argue that these changes > are taking care of an undefined situation (real hardware will always > have the IPIB set). > > As long as the architecture is not violated, I can live with the > proposed changes. Thanks! > I however would like to point out that this only > covers a corner case (no -boot or -device ..,bootindex specified). Sure. We™ should/could maybe also add some more documentation to https://www.qemu.org/docs/master/system/target-s390x.html to make it more clear to the "unexperienced" qemu-system-s390x users that "bootindex" is the preferred / architected way of booting there. > Please don't create the impression that this patches will lead to the > same behavior as on other platforms. Ok, I'll try to state that more clearly in the cover letter of v2. Thomas