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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:54582) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qyvIX-0005cb-1Y; Fri, 03 Nov 2023 14:37:21 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1qyvIY-0008Tw-8D; Fri, 03 Nov 2023 14:37:22 +0000 Date: Fri, 3 Nov 2023 14:37:22 +0000 From: "Russell King (Oracle)" To: Gavin Shan Cc: James Morse , linux-pm@vger.kernel.org, loongarch@lists.linux.dev, linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev, x86@kernel.org, Salil Mehta , Jean-Philippe Brucker , jianyong.wu@arm.com, justin.he@arm.com Subject: Re: [RFC PATCH v2 22/35] ACPI: Check _STA present bit before making CPUs not present Message-ID: References: <20230913163823.7880-1-james.morse@arm.com> <20230913163823.7880-23-james.morse@arm.com> <518859b1-64a9-d723-963c-56c7f6fc2da1@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <518859b1-64a9-d723-963c-56c7f6fc2da1@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231103_073732_774918_7E611DF1 X-CRM114-Status: GOOD ( 34.96 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Sep 19, 2023 at 10:45:39AM +1000, Gavin Shan wrote: > On 9/14/23 02:38, James Morse wrote: > > When called acpi_processor_post_eject() unconditionally make a CPU > > not-present and unregisters it. > > > > To add support for AML events where the CPU has become disabled, but > > remains present, the _STA method should be checked before calling > > acpi_processor_remove(). > > > > Rename acpi_processor_post_eject() acpi_processor_remove_possible(), and > > check the _STA before calling. > > > > Adding the function prototype for arch_unregister_cpu() allows the > > preprocessor guards to be removed. > > > > After this change CPUs will remain registered and visible to > > user-space as offline if buggy firmware triggers an eject-request, > > but doesn't clear the corresponding _STA bits after _EJ0 has been > > called. > > > > Signed-off-by: James Morse > > --- > > drivers/acpi/acpi_processor.c | 31 +++++++++++++++++++++++++------ > > include/linux/cpu.h | 1 + > > 2 files changed, 26 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c > > index 00dcc23d49a8..2cafea1edc24 100644 > > --- a/drivers/acpi/acpi_processor.c > > +++ b/drivers/acpi/acpi_processor.c > > @@ -457,13 +457,12 @@ static int acpi_processor_add(struct acpi_device *device, > > return result; > > } > > -#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU > > /* Removal */ > > -static void acpi_processor_post_eject(struct acpi_device *device) > > +static void acpi_processor_make_not_present(struct acpi_device *device) > > { > > struct acpi_processor *pr; > > - if (!device || !acpi_driver_data(device)) > > + if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU)) > > return; > > In order to use IS_ENABLED(), And the rest of this statement is where? > > pr = acpi_driver_data(device); > > @@ -501,7 +500,29 @@ static void acpi_processor_post_eject(struct acpi_device *device) > > free_cpumask_var(pr->throttling.shared_cpu_map); > > kfree(pr); > > } > > -#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */ > > + > > +static void acpi_processor_post_eject(struct acpi_device *device) > > +{ > > + struct acpi_processor *pr; > > + unsigned long long sta; > > + acpi_status status; > > + > > + if (!device) > > + return; > > + > > + pr = acpi_driver_data(device); > > + if (!pr || pr->id >= nr_cpu_ids || invalid_phys_cpuid(pr->phys_id)) > > + return; > > + > > Do we really need to validate the logic and hardware CPU IDs here? I think > the ACPI processor device can't be added successfully if one of them is > invalid. > > > + status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta); > > + if (ACPI_FAILURE(status)) > > + return; > > + > > + if (cpu_present(pr->id) && !(sta & ACPI_STA_DEVICE_PRESENT)) { > > + acpi_processor_make_not_present(device); > > + return; > > + } > > +} > > #ifdef CONFIG_ARCH_MIGHT_HAVE_ACPI_PDC > > bool __init processor_physically_present(acpi_handle handle) > > @@ -626,9 +647,7 @@ static const struct acpi_device_id processor_device_ids[] = { > > static struct acpi_scan_handler processor_handler = { > > .ids = processor_device_ids, > > .attach = acpi_processor_add, > > -#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU > > .post_eject = acpi_processor_post_eject, > > -#endif > > .hotplug = { > > .enabled = true, > > }, > > diff --git a/include/linux/cpu.h b/include/linux/cpu.h > > index a71691d7c2ca..e117c06e0c6b 100644 > > --- a/include/linux/cpu.h > > +++ b/include/linux/cpu.h > > @@ -81,6 +81,7 @@ struct device *cpu_device_create(struct device *parent, void *drvdata, > > const struct attribute_group **groups, > > const char *fmt, ...); > > extern int arch_register_cpu(int cpu); > > +extern void arch_unregister_cpu(int cpu); > > arch_unregister_cpu() is protected by CONFIG_HOTPLUG_CPU in the individual architectures, > for example arch/ia64/kernel/topology.c Yes, I agree, there _may_ be a reference to arch_unregister_cpu() if the compiler doesn't optimise the "if(0) return". As things stand in my "head" tree (which I'll be posting once 6.7-rc1 is out) at the point that this patch exists in the series, there are no architectures which provide arch_unregister_cpu(), and the only implementation of it is the __weak one in drivers/base/cpu.c That implementation is also ifdef'd with CONFIG_HOTPLUG_CPU and also CONFIG_GENERIC_CPU_DEVICES. Meanwhile, acpi_processor.c is always built with ACPI, and while we have IS_ENABLED() clauses with James' patches for both of these symbols, if the compiler doesn't optimise the code away, we will end up with a reference and a link-time error. That being said, the 0-day bot has not reported anything as yet (and it builds my tree.) So, is this a problem that needs to be solved or not? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel