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[176.184.32.47]) by smtp.gmail.com with ESMTPSA id bg30-20020a05600c3c9e00b0040d62f89381sm4924090wmb.35.2024.01.09.13.22.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Jan 2024 13:22:34 -0800 (PST) Message-ID: <2fa344b7-ccd2-4e6a-8c32-5ad7e4c960d6@linaro.org> Date: Tue, 9 Jan 2024 22:22:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/33] hw/cpu/arm: Remove one use of qemu_get_cpu() in A7/A15 MPCore priv Content-Language: en-US To: Fabiano Rosas , =?UTF-8?Q?C=C3=A9dric_Le_Goater?= , qemu-devel@nongnu.org, Markus Armbruster , =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: Paolo Bonzini , Tyrone Ting , =?UTF-8?Q?Alex_Benn=C3=A9e?= , Manos Pitsidianakis , Eduardo Habkost , Joel Stanley , Alistair Francis , Anton Johansson , Andrey Smirnov , Peter Maydell , Hao Wu , Jean-Christophe Dubois , Igor Mitsyanko , "Edgar E. Iglesias" , Andrew Jeffery , Rob Herring , qemu-arm@nongnu.org, Mark Cave-Ayland , Peter Xu References: <20231212162935.42910-1-philmd@linaro.org> <03b969d3-1947-4186-b3ee-15e3cddc5f34@kaod.org> <18a38b88-8f20-420c-9916-a03d1b4930a7@linaro.org> <38cfa9de-874b-41dd-873e-5ad1f5a5805e@kaod.org> <87y1d6i47m.fsf@suse.de> <597186d9-af21-46e8-8075-f21d36c01c07@kaod.org> <87plya76cu.fsf@suse.de> <87bk9u8dhs.fsf@suse.de> From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= In-Reply-To: <87bk9u8dhs.fsf@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::333; envelope-from=philmd@linaro.org; helo=mail-wm1-x333.google.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi Fabiano, On 9/1/24 21:21, Fabiano Rosas wrote: > Cédric Le Goater writes: > >> On 1/9/24 18:40, Fabiano Rosas wrote: >>> Cédric Le Goater writes: >>> >>>> On 1/3/24 20:53, Fabiano Rosas wrote: >>>>> Philippe Mathieu-Daudé writes: >>>>> >>>>>> +Peter/Fabiano >>>>>> >>>>>> On 2/1/24 17:41, Cédric Le Goater wrote: >>>>>>> On 1/2/24 17:15, Philippe Mathieu-Daudé wrote: >>>>>>>> Hi Cédric, >>>>>>>> >>>>>>>> On 2/1/24 15:55, Cédric Le Goater wrote: >>>>>>>>> On 12/12/23 17:29, Philippe Mathieu-Daudé wrote: >>>>>>>>>> Hi, >>>>>>>>>> >>>>>>>>>> When a MPCore cluster is used, the Cortex-A cores belong the the >>>>>>>>>> cluster container, not to the board/soc layer. This series move >>>>>>>>>> the creation of vCPUs to the MPCore private container. >>>>>>>>>> >>>>>>>>>> Doing so we consolidate the QOM model, moving common code in a >>>>>>>>>> central place (abstract MPCore parent). >>>>>>>>> >>>>>>>>> Changing the QOM hierarchy has an impact on the state of the machine >>>>>>>>> and some fixups are then required to maintain migration compatibility. >>>>>>>>> This can become a real headache for KVM machines like virt for which >>>>>>>>> migration compatibility is a feature, less for emulated ones. >>>>>>>> >>>>>>>> All changes are either moving properties (which are not migrated) >>>>>>>> or moving non-migrated QOM members (i.e. pointers of ARMCPU, which >>>>>>>> is still migrated elsewhere). So I don't see any obvious migration >>>>>>>> problem, but I might be missing something, so I Cc'ed Juan :> >>>>> >>>>> FWIW, I didn't spot anything problematic either. >>>>> >>>>> I've ran this through my migration compatibility series [1] and it >>>>> doesn't regress aarch64 migration from/to 8.2. The tests use '-M >>>>> virt -cpu max', so the cortex-a7 and cortex-a15 are not covered. I don't >>>>> think we even support migration of anything non-KVM on arm. >>>> >>>> it happens we do. >>>> >>> >>> Oh, sorry, I didn't mean TCG here. Probably meant to say something like >>> non-KVM-capable cpus, as in 32-bit. Nevermind. >> >> Theoretically, we should be able to migrate to a TCG guest. Well, this >> worked in the past for PPC. When I was doing more KVM related changes, >> this was very useful for dev. Also, some machines are partially emulated. >> Anyhow I agree this is not a strong requirement and we often break it. >> Let's focus on KVM only. >> >>>>> 1- https://gitlab.com/farosas/qemu/-/jobs/5853599533 >>>> >>>> yes it depends on the QOM hierarchy and virt seems immune to the changes. >>>> Good. >>>> >>>> However, changing the QOM topology clearly breaks migration compat, >>> >>> Well, "clearly" is relative =) You've mentioned pseries and aspeed >>> already, do you have a pointer to one of those cases were we broke >>> migration >> >> Regarding pseries, migration compat broke because of 5bc8d26de20c >> ("spapr: allocate the ICPState object from under sPAPRCPUCore") which >> is similar to the changes proposed by this series, it impacts the QOM >> hierarchy. Here is the workaround/fix from Greg : 46f7afa37096 >> ("spapr: fix migration of ICPState objects from/to older QEMU") which >> is quite an headache and this turned out to raise another problem some >> months ago ... :/ That's why I sent [1] to prepare removal of old >> machines and workarounds becoming a burden. > > This feels like something that could be handled by the vmstate code > somehow. The state is there, just under a different path. What, the QOM path is used in migration? ... See recent discussions on "QOM path stability": https://lore.kernel.org/qemu-devel/ZZfYvlmcxBCiaeWE@redhat.com/ https://lore.kernel.org/qemu-devel/87jzojbxt7.fsf@pond.sub.org/ https://lore.kernel.org/qemu-devel/87v883by34.fsf@pond.sub.org/ > No one wants > to be policing QOM hierarchy changes in every single series that shows > up on the list. > > Anyway, thanks for the pointers. I'll study that code a bit more, maybe > I can come up with some way to handle these cases. > > Hopefully between the analyze-migration test and the compat tests we'll > catch the next bug of this kind before it gets merged. > >