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Thu, 29 Apr 2021 08:08:21 +0200 (CEST) From: Markus Armbruster To: Stefan Hajnoczi Subject: Re: [PATCH] hw/ide: Fix crash when plugging a piix3-ide device into the x-remote machine References: <20210416125256.2039734-1-thuth@redhat.com> <4c1c6e99-066e-f916-31dc-acb50caa5320@redhat.com> <5bbdc5d9-692e-63bb-2ad6-38a5711c4021@redhat.com> <9714a87d-95f7-a6f0-4c35-a7e9d1aa1144@redhat.com> <87mtti1oie.fsf@dusky.pond.sub.org> Date: Thu, 29 Apr 2021 08:08:21 +0200 In-Reply-To: (Stefan Hajnoczi's message of "Wed, 28 Apr 2021 19:43:18 +0100") Message-ID: <87h7jpipwq.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.22, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Elena Ufimtseva , John G Johnson , Thomas Huth , Jagannathan Raman , qemu-block@nongnu.org, Peter Maydell , John Snow , qemu-devel@nongnu.org, Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Stefan Hajnoczi writes: > On Wed, Apr 28, 2021 at 04:18:17PM +0200, Markus Armbruster wrote: >> Stefan Hajnoczi writes: [...] >> > The approach in this patch is okay but we should keep in mind it only >> > solves piix3-ide. ISA provides a non-qdev backdoor API and there may be >> > more instances of this type of bug. >> > >> > A qdev fix would address the root cause and make it possible to drop the >> > backdoor API, but that's probably too much work for little benefit. >> >> What do you mean by backdoor API? Global @isabus? > > Yes. It's also strange that isa_get_irq(ISADevice *dev, unsigned isairq) > accepts dev = NULL as a valid argument. @isabus is static in hw/isa/isa-bus.c. Uses: * Limit isa_bus_new() to one ISA bus. Arbitrary restriction; multiple ISA buses could work with suitable memory mapping and IRQ wiring. "Single ISA bus" assumptions could of course hide elsewhere in the code. * Implied argument to isa_get_irq(), isa_register_ioport(), isa_register_portio_list(), isa_address_space(), isa_address_space_io(). isa_get_irq() asserts that a non-null @dev is a child of @isabus. This means we don't actually need @isabus, except when @dev is null. I suspect two separate functions would be cleaner: one taking an ISABus * argument, and a wrapper taking an ISADevice * argument. isa_address_space() and isa_address_space_io() work the same, less the assertion. isa_register_ioport() and isa_register_portio_list() take a non-null @dev argument. They don't actually need @isabus. To eliminate global @isabus, we need to fix up the callers passing null @dev. Clean solution: plumb the ISABus returned by isa_bus_new() to the call sites. Where that's impractical, we can also get it from QOM, like build_dsdt_microvm() does.