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Re: [PATCH v3 13/24] arm64: Populate cpuinfo after notify_cpu_starting

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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





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[PATCH v3 00/24] arm64: Consolidate CPU feature handling "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:30 +0200
  [PATCH v3 23/24] arm64: Expose feature registers by emulating MRS "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:30 +0200
  [PATCH v3 13/24] arm64: Populate cpuinfo after notify_cpu_starting "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:40 +0200
    Re: [PATCH v3 13/24] arm64: Populate cpuinfo after  notify_cpu_starting Catalin Marinas <catalin.marinas@arm.com> - 2015-10-15 13:00 +0200
      Re: [PATCH v3 13/24] arm64: Populate cpuinfo after  notify_cpu_starting "Suzuki K. Poulose" <Suzuki.Poulose@arm.com> - 2015-10-15 15:30 +0200
  [PATCH v3 04/24] arm64: Move cpu feature detection code "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:40 +0200
  [PATCH v3 08/24] arm64: Handle width of a cpuid feature "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:40 +0200
  [PATCH v3 12/24] arm64: Cleanup mixed endian support detection "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:40 +0200
  [PATCH v3 19/24] arm64/kvm: Make use of the system wide safe values "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:40 +0200
  [PATCH v3 06/24] arm64: Move /proc/cpuinfo handling code "Suzuki K. Poulose" <suzuki.poulose@arm.com> - 2015-10-13 19:40 +0200
  Re: [PATCH v3 00/24] arm64: Consolidate CPU feature handling Dave Martin <Dave.Martin@arm.com> - 2015-10-16 17:20 +0200
    Re: [PATCH v3 00/24] arm64: Consolidate CPU feature handling "Suzuki K. Poulose" <Suzuki.Poulose@arm.com> - 2015-10-16 17:40 +0200
      Re: [PATCH v3 00/24] arm64: Consolidate CPU feature handling Dave Martin <Dave.Martin@arm.com> - 2015-10-16 17:50 +0200

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