Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 18 Dec 2023 21:22:03 +0100 | Subject | Re: [PATCH RFC v3 03/21] ACPI: processor: Register CPUs that are online, but not described in the DSDT |
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On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@armlinux.org.uk> wrote: > > From: James Morse <james.morse@arm.com> > > ACPI has two descriptions of CPUs, one in the MADT/APIC table, the other > in the DSDT. Both are required. (ACPI 6.5's 8.4 "Declaring Processors" > says "Each processor in the system must be declared in the ACPI > namespace"). Having two descriptions allows firmware authors to get > this wrong. > > If CPUs are described in the MADT/APIC, they will be brought online > early during boot. Once the register_cpu() calls are moved to ACPI, > they will be based on the DSDT description of the CPUs. When CPUs are > missing from the DSDT description, they will end up online, but not > registered. > > Add a helper that runs after acpi_init() has completed to register > CPUs that are online, but weren't found in the DSDT. Any CPU that > is registered by this code triggers a firmware-bug warning and kernel > taint. > > Qemu TCG only describes the first CPU in the DSDT, unless cpu-hotplug > is configured.
So why is this a kernel problem?
> Signed-off-by: James Morse <james.morse@arm.com> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> > Reviewed-by: Gavin Shan <gshan@redhat.com> > Tested-by: Miguel Luis <miguel.luis@oracle.com> > Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com> > Tested-by: Jianyong Wu <jianyong.wu@arm.com> > Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> > --- > drivers/acpi/acpi_processor.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c > index 6a542e0ce396..0511f2bc10bc 100644 > --- a/drivers/acpi/acpi_processor.c > +++ b/drivers/acpi/acpi_processor.c > @@ -791,6 +791,25 @@ void __init acpi_processor_init(void) > acpi_pcc_cpufreq_init(); > } > > +static int __init acpi_processor_register_missing_cpus(void) > +{ > + int cpu; > + > + if (acpi_disabled) > + return 0; > + > + for_each_online_cpu(cpu) { > + if (!get_cpu_device(cpu)) { > + pr_err_once(FW_BUG "CPU %u has no ACPI namespace description!\n", cpu); > + add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK); > + arch_register_cpu(cpu);
Which part of this code is related to ACPI?
> + } > + } > + > + return 0; > +} > +subsys_initcall_sync(acpi_processor_register_missing_cpus); > + > #ifdef CONFIG_ACPI_PROCESSOR_CSTATE > /** > * acpi_processor_claim_cst_control - Request _CST control from the platform. > --
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