| Message ID | 1444756952-31145-14-git-send-email-suzuki.poulose@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Oct 13, 2015 at 06:22:21PM +0100, Suzuki K. Poulose wrote: > This patch delays populating the cpuinfo for a new (hotplugged) > CPU until the notifiers have executed. This will enable us to verify > if the new (hotplugged) CPU has all the capabilities which the system > already has. If it doesn't, we could prevent it from turning online and > also modifying the system wide feature register status. Just a question here: do we expect the notifiers to enable certain features that we check later? AFAICT, the checking is done on the feature registers which don't change after notifiers, so we could as well block the booting before any notifier is run.
On 15/10/15 11:54, Catalin Marinas wrote: > On Tue, Oct 13, 2015 at 06:22:21PM +0100, Suzuki K. Poulose wrote: >> This patch delays populating the cpuinfo for a new (hotplugged) >> CPU until the notifiers have executed. This will enable us to verify >> if the new (hotplugged) CPU has all the capabilities which the system >> already has. If it doesn't, we could prevent it from turning online and >> also modifying the system wide feature register status. > > Just a question here: do we expect the notifiers to enable certain > features that we check later? AFAICT, the checking is done on the > feature registers which don't change after notifiers, No. The notifiers are registered only after we compute the cpu capabilities (at which point all the boot time activated CPUs are turned on and has updated their cpuinfo). The features won't change after this point throughout the lifetime of the system. So we don't want to run the capability check for the 'CPUs' during the normal boot up. It is only for the hotplug case. We compute the capability based on the booted CPUs from smp_cpus_done() and then apply the alternatives based on what we have in common. So the system can function properly with mismatched features from the CPUs. But if a new CPU is brought online with at least one missing established capability, we should fail the bring up. so we could as > well block the booting before any notifier is run. > Thanks Suzuki
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index 3b22e65..4a36eb6 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -145,9 +145,6 @@ asmlinkage void secondary_start_kernel(void) cpumask_set_cpu(cpu, mm_cpumask(mm)); set_my_cpu_offset(per_cpu_offset(smp_processor_id())); - pr_info("CPU%u: Booted secondary processor [%08x]\n", - cpu, read_cpuid_id()); - /* * TTBR0 is only used for the identity mapping at this stage. Make it * point to zero page to avoid speculatively fetching new entries. @@ -163,14 +160,14 @@ asmlinkage void secondary_start_kernel(void) cpu_ops[cpu]->cpu_postboot(); /* - * Log the CPU info before it is marked online and might get read. + * Enable GIC and timers. */ - cpuinfo_store_cpu(); + notify_cpu_starting(cpu); /* - * Enable GIC and timers. + * Log the CPU info before it is marked online and might get read. */ - notify_cpu_starting(cpu); + cpuinfo_store_cpu(); smp_store_cpu_info(cpu); @@ -179,6 +176,10 @@ asmlinkage void secondary_start_kernel(void) * the CPU migration code to notice that the CPU is online * before we continue. */ + + pr_info("CPU%u: Booted secondary processor [%08x]\n", + cpu, read_cpuid_id()); + set_cpu_online(cpu, true); complete(&cpu_running);
This patch delays populating the cpuinfo for a new (hotplugged) CPU until the notifiers have executed. This will enable us to verify if the new (hotplugged) CPU has all the capabilities which the system already has. If it doesn't, we could prevent it from turning online and also modifying the system wide feature register status. Also delays advertising that the CPU has booted until we complete the notifiers, when we are ready to mark it online. This would avoid confusing the user if the CPU fails to boot due to a missing capability. Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com> --- arch/arm64/kernel/smp.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)