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[221.241.217.81]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-77f0ef2db80sm1846205b3a.24.2025.09.19.16.46.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Sep 2025 16:46:17 -0700 (PDT) Date: Sat, 20 Sep 2025 08:46:14 +0900 Message-ID: From: Hajime Tazaki To: johannes@sipsolutions.net Cc: linux-um@lists.infradead.org, ricarkol@google.com, Liam.Howlett@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND v11 10/13] um: nommu: a work around for MMU dependency to PCI driver In-Reply-To: References: <4a9dde10c586883d20a8201ca7d76e6d7d52eaf4.1758181109.git.thehajime@gmail.com> <6b1abe384237c8129e8043ecdfdad77758d2fd2f.camel@sipsolutions.net> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII thanks Johannes, I think I got a clearer view than before. I guess Kconfig does the right thing. And Kunit does the right too but an additional job which Kunit does prevents run tests w/ !MMU. > > CONIFG_MMU=n > > > > via --kconfig_add CONFIG_MMU=n. > > Sure. But that should disable CONFIG_UML_PCI_OVER_VIRTIO, and it doesn't > now. Kconfig (via kunit.py config) disables CONFIG_UML_PCI_OVER_VIRTIO correctly. But after that, Kunit does the additional job, validate_config() (in kunit_kernel.py), which checks the configs (arch_uml.config + --kconfig_add) is a subset of the final result of .config. When I applied a patch below: diff --git a/arch/um/drivers/Kconfig b/arch/um/drivers/Kconfig index 6a0354ca032f..04025207a077 100644 --- a/arch/um/drivers/Kconfig +++ b/arch/um/drivers/Kconfig @@ -159,6 +159,7 @@ config UML_RTC config UML_PCI bool + depends on MMU select FORCE_PCI select IRQ_MSI_LIB select UML_IOMEM_EMULATION @@ -170,6 +171,7 @@ config UML_PCI_OVER_VIRTIO bool "Enable PCI over VIRTIO device simulation" # in theory, just VIRTIO is enough, but that causes recursion depends on VIRTIO_UML + depends on MMU select UML_PCI and do ./tools/testing/kunit/kunit.py config --kconfig_add CONFIG_MMU=n the validation currently gives the following error: ERROR:root:Not all Kconfig options selected in kunitconfig were in the generated .config. This is probably due to unsatisfied dependencies. Missing: CONFIG_UML_PCI_OVER_VIRTIO=y Note: many Kconfig options aren't available on UML. You can try running on a different architecture with something like "--arch=x86_64". so, if I give an additional --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=n to the command line, the validation passes, because the configs (arch_uml.config + --kconfig_add) becomes the subset of the final result. what I can handle this would be either of them: 1) use --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=n when using kunit w/ !MMU, and drop this patch from the series (no modification to the tree) 2) prepare a different file for !MMU & ARCH=um testing (e.g., arch_uml_nommu.config), and add an option to kunit.py to switch MMU or !MMU 3) implement virtio-pci for !MMU and propose to remove the restriction of CONFIG_PCI depends on CONFIG_MMU. 2) will be removed when 3) is done so, I'm hesitating to propose a patch used by whole tree. so, I think 1) is (not the best but) a reasonable solution, with a note in nommu-uml specific document (i.e., [PATCH 12/13]). Let me know what you think. -- Hajime On Fri, 19 Sep 2025 18:38:03 +0900, Johannes Berg wrote: > > On Fri, 2025-09-19 at 18:32 +0900, Hajime Tazaki wrote: > > currently, drivers/pci/Kconfig (CONFIG_PCI) marks as depends on MMU, > > Right. > > > so we cannot select it when CONFIG_MMU=n. > > Actually, I believe that's not true, I think it *can* select something > even if you override the 'depends on' it has, it just causes a warning > in Kconfig. > > But I don't think PCI is even selected, UML_PCI is selected, and then > that selects PCI_MSI which should really only be reachable when PCI is > enabled, so this perhaps does nothing? Not sure ... > > > but it's different with kunit when using them via kunit.py config, > > It really isn't, you just don't see everything because kunit.py hides > the build from you. > > > it first adds > > > > CONFIG_VIRTIO_UML=y > > CONFIG_UML_PCI_OVER_VIRTIO=y > > > > via tools/testing/kunit/configs/arch_uml.config, and then add > > > > CONIFG_MMU=n > > > > via --kconfig_add CONFIG_MMU=n. > > Sure. But that should disable CONFIG_UML_PCI_OVER_VIRTIO, and it doesn't > now. > > > and then execute make ARCH=um olddefconfig, which in turn enables > > CONFIG_UML_PCI_OVER_VIRTIO. > > Keeps it, let's say. > > > if we append "--kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=n" to kunit.py, > > it will overwrite the arch_uml.config. > > Yeah but that being required doesn't make sense - the Kconfig should > express the correct dependencies. > > > # I don't know how kunit handles those appended CONFIG entries, though.. > > It just puts them into the file and runs oldconfig, I guess? > > > my goal is simple; to test !MMU code via kunit. > > Sure. > > > my original patch or the additional kconfig argument (--kconfig_add) > > satisfies this goal. > > Sure. But both are the wrong solution, as I said, the Kconfig should > express the correct dependencies. > > > > The problem is probably UML_PCI_OVER_VIRTIO selecting UML_PCI selecting > > > various PCI code, but nothing depends on PCI in the first place. Which > > > it should, then? > > > > I don't understand the 'nothing depends on PCI...' part. care to > > elaborate ? > > See above, I think? > > My gut feeling is that UML_PCI_OVER_VIRTIO should depend on PCI but I > don't know if that then doesn't end up in some kind of circular > dependency. > > johannes