Re: [PATCH v7 11/16] irqchip/gic-v3: Add support for ACPI's disabled but 'online capable' CPUs

[Jonathan Cameron]

On Wed, 24 Apr 2024 18:08:30 +0100
Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote:

> On Wed, 24 Apr 2024 17:35:54 +0100
> Salil Mehta <salil.mehta@xxxxxxxxxx> wrote:
> 
> > >  From: Marc Zyngier <maz@xxxxxxxxxx>
> > >  Sent: Wednesday, April 24, 2024 4:33 PM
> > >  To: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> > >  Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Peter Zijlstra
> > >  <peterz@xxxxxxxxxxxxx>; linux-pm@xxxxxxxxxxxxxxx;
> > >  loongarch@xxxxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx; linux-
> > >  arch@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> > >  kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx;
> > >  Russell King <linux@xxxxxxxxxxxxxxx>; Rafael J . Wysocki
> > >  <rafael@xxxxxxxxxx>; Miguel Luis <miguel.luis@xxxxxxxxxx>; James Morse
> > >  <james.morse@xxxxxxx>; Salil Mehta <salil.mehta@xxxxxxxxxx>; Jean-
> > >  Philippe Brucker <jean-philippe@xxxxxxxxxx>; Catalin Marinas
> > >  <catalin.marinas@xxxxxxx>; Will Deacon <will@xxxxxxxxxx>; Linuxarm
> > >  <linuxarm@xxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; Borislav
> > >  Petkov <bp@xxxxxxxxx>; Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>;
> > >  justin.he@xxxxxxx; jianyong.wu@xxxxxxx
> > >  Subject: Re: [PATCH v7 11/16] irqchip/gic-v3: Add support for ACPI's
> > >  disabled but 'online capable' CPUs
> > >  
> > >  On Wed, 24 Apr 2024 13:54:38 +0100,
> > >  Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote:    
> > >  >
> > >  > On Tue, 23 Apr 2024 13:01:21 +0100
> > >  > Marc Zyngier <maz@xxxxxxxxxx> wrote:
> > >  >    
> > >  > > On Mon, 22 Apr 2024 11:40:20 +0100,
> > >  > > Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote:    
> > >  > > >
> > >  > > > On Thu, 18 Apr 2024 14:54:07 +0100 Jonathan Cameron
> > >  > > > <Jonathan.Cameron@xxxxxxxxxx> wrote:    
> > >  
> > >  [...]
> > >      
> > >  > > >    
> > >  > > > > +	/*
> > >  > > > > +	 * Capable but disabled CPUs can be brought online later.  What about
> > >  > > > > +	 * the redistributor? ACPI doesn't want to say!
> > >  > > > > +	 * Virtual hotplug systems can use the MADT's "always-on"  GICR entries.
> > >  > > > > +	 * Otherwise, prevent such CPUs from being brought online.
> > >  > > > > +	 */
> > >  > > > > +	if (!(gicc->flags & ACPI_MADT_ENABLED)) {
> > >  > > > > +		pr_warn_once("CPU %u's redistributor is  inaccessible: this CPU can't be brought online\n", cpu);
> > >  > > > > +		set_cpu_present(cpu, false);
> > >  > > > > +		set_cpu_possible(cpu, false);    
> > 
> > (a digression) shouldn't we be clearing the enabled mask as well?
> > 
> >                                           set_cpu_enabled(cpu, false);  
> 
> FWIW I think not necessary. enabled is only set in register_cpu() and aim here is to
> never call that for CPUs in this state.
> 
> Anyhow, I got distracted by the firmware bug I found whilst trying to test this but
> now have a test setup that hits this path (once deliberately broken), so will
> see what we can do about that doesn't have affect those masks.

This may be relevant with the context of Marc's email.  Don't crop so much!
However I think we probably don't care. This is bios bug, if we miss report it such
that userspace thinks it can online something that work work, it probably doesn't
matter.

Jonathan

> 
> Jonathan
> 
> 
> > 
> > 
> > Best regards
> > Salil  
> 
> 
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