Messages in this thread | | | Subject | Re: [PATCH] arm64/cpuinfo: Drop boot_cpu_data | From | Anshuman Khandual <> | Date | Mon, 4 May 2020 20:23:08 +0530 |
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On 05/04/2020 06:13 PM, Mark Rutland wrote: > On Mon, May 04, 2020 at 06:00:00PM +0530, Anshuman Khandual wrote: >> A global boot_cpu_data is not really required. Lets drop this. > > I don't think it's true that this isn't required today. > > One reason that we have both boot_cpu_data and a cpu_data variable for > CPU0 is that CPU0 itself can be hotplugged out then back in, and this > allows us to detect if CPU0's features have changed (e.g. due to FW > failing to configure it appropriately, or real physical hotplug > occurring).
Understood. After hotplug, CPU0 will come back via secondary_start_kernel() where it's current register values will be checked against earlier captured values i.e boot_cpu_data.
But wondering why should CPU0 be treated like any other secondary CPU. IOW in case the fresh boot CPU register values dont match with boot_cpu_data, should not the online process just be declined ? AFAICS, current approach will let the kernel run with taint in case of a mismatch.
> > So NAK to the patch as it stands. If we're certain we capture all of > those details even without boot_cpu_data, then we should make other > changes to make that clear (e.g. removing it as an argument to > update_cpu_features()).
There might not be another way, unless we can override CPU0's cpu_data variable when the boot CPU comes back in after vetting against existing values. Is there any particular reason to store the very first boot CPU0 info for ever ?
Passing on CPU0's cpu_data variable in update_cpu_features() for secondary CPUs during boot still make sense. It helps in finalizing register values. Re-entering CPU0's test against boot_cpu_data seems different.
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