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SubjectRe: [PATCH v7 11/16] irqchip/gic-v3: Add support for ACPI's disabled but 'online capable' CPUs
On Wed, 24 Apr 2024 17:35:54 +0100
Salil Mehta <salil.mehta@huawei.com> wrote:

> > From: Marc Zyngier <maz@kernel.org>
> > Sent: Wednesday, April 24, 2024 4:33 PM
> > To: Jonathan Cameron <jonathan.cameron@huawei.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>; Peter Zijlstra
> > <peterz@infradead.org>; linux-pm@vger.kernel.org;
> > loongarch@lists.linux.dev; linux-acpi@vger.kernel.org; linux-
> > arch@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
> > kernel@lists.infradead.org; kvmarm@lists.linux.dev; x86@kernel.org;
> > Russell King <linux@armlinux.org.uk>; Rafael J . Wysocki
> > <rafael@kernel.org>; Miguel Luis <miguel.luis@oracle.com>; James Morse
> > <james.morse@arm.com>; Salil Mehta <salil.mehta@huawei.com>; Jean-
> > Philippe Brucker <jean-philippe@linaro.org>; Catalin Marinas
> > <catalin.marinas@arm.com>; Will Deacon <will@kernel.org>; Linuxarm
> > <linuxarm@huawei.com>; Ingo Molnar <mingo@redhat.com>; Borislav
> > Petkov <bp@alien8.de>; Dave Hansen <dave.hansen@linux.intel.com>;
> > justin.he@arm.com; jianyong.wu@arm.com
> > 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@huawei.com> wrote:
> > >
> > > On Tue, 23 Apr 2024 13:01:21 +0100
> > > Marc Zyngier <maz@kernel.org> wrote:
> > >
> > > > On Mon, 22 Apr 2024 11:40:20 +0100,
> > > > Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:
> > > > >
> > > > > On Thu, 18 Apr 2024 14:54:07 +0100 Jonathan Cameron
> > > > > <Jonathan.Cameron@huawei.com> 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.

Jonathan


>
>
> Best regards
> Salil


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