On Thu, 25 Apr 2024 13:31:50 +0100
Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote:
> On Wed, 24 Apr 2024 16:33:22 +0100
> Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> > 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);
> > > > > > + return 0;
> > > > > > + }
> > > >
> > > > It seems dangerous to clear those this late in the game, given how
> > > > disconnected from the architecture code this is. Are we sure that
> > > > nothing has sampled these cpumasks beforehand?
> > >
> > > Hi Marc,
> > >
> > > Any firmware that does this is being considered as buggy already
> > > but given it is firmware and the spec doesn't say much about this,
> > > there is always the possibility.
> >
> > There is no shortage of broken firmware out there, and I expect this
> > trend to progress.
> >
> > > Not much happens between the point where these are setup and
> > > the point where the the gic inits and this code runs, but even if careful
> > > review showed it was fine today, it will be fragile to future changes.
> > >
> > > I'm not sure there is a huge disadvantage for such broken firmware in
> > > clearing these masks from the point of view of what is used throughout
> > > the rest of the kernel. Here I think we are just looking to prevent the CPU
> > > being onlined later.
> >
> > I totally agree on the goal, I simply question the way you get to it.
> >
> > >
> > > We could add a set_cpu_broken() with appropriate mask.
> > > Given this is very arm64 specific I'm not sure Rafael will be keen on
> > > us checking such a mask in the generic ACPI code, but we could check it in
> > > arch_register_cpu() and just not register the cpu if it matches.
> > > That will cover the vCPU hotplug case.
> > >
> > > Does that sounds sensible, or would you prefer something else?
> >
> >
> > Such a 'broken_rdists' mask is exactly what I have in mind, just
> > keeping it private to the GIC driver, and not expose it anywhere else.
> > You can then fail the hotplug event early, and avoid changing the
> > global masks from within the GIC driver. At least, we don't mess with
> > the internals of the kernel, and the CPU is properly marked as dead
> > (that mechanism should already work).
> >
> > I'd expect the handling side to look like this (will not compile, but
> > you'll get the idea):
> Hi Marc,
>
> In general this looks good - but...
>
> I haven't gotten to the bottom of why yet (and it might be a side
> effect of how I hacked the test by lying in minimal fashion and
> just frigging the MADT read functions) but the hotplug flow is only getting
> as far as calling __cpu_up() before it seems to enter an infinite loop.
> That is it never gets far enough to fail this test.
>
> Getting stuck in a psci cpu_on call. I'm guessing something that
> we didn't get to in the earlier gicv3 calls before bailing out is blocking that?
> Looks like it gets to
> SMCCC smc
> and is never seen again.
>
> Any ideas on where to look? The one advantage so far of the higher level
> approach is we never tried the hotplug callbacks at all so avoided hitting
> that call. One (little bit horrible) solution that might avoid this would
> be to add another cpuhp state very early on and fail at that stage.
> I'm not keen on doing that without a better explanation than I have so far!
Whilst it still doesn't work I suspect I'm loosing ability to print to the console
between that point and somewhat later and real problem is elsewhere.
Jonathan
>
> Thanks,
>
> J
>
>
> > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > index 6fb276504bcc..e8f02bfd0e21 100644
> > --- a/drivers/irqchip/irq-gic-v3.c
> > +++ b/drivers/irqchip/irq-gic-v3.c
> > @@ -1009,6 +1009,9 @@ static int __gic_populate_rdist(struct redist_region *region, void __iomem *ptr)
> > u64 typer;
> > u32 aff;
> >
> > + if (cpumask_test_cpu(smp_processor_id(), &broken_rdists))
> > + return 1;
> > +
> > /*
> > * Convert affinity to a 32bit value that can be matched to
> > * GICR_TYPER bits [63:32].
> > @@ -1260,14 +1263,15 @@ static int gic_dist_supports_lpis(void)
> > !gicv3_nolpi);
> > }
> >
> > -static void gic_cpu_init(void)
> > +static int gic_cpu_init(void)
> > {
> > void __iomem *rbase;
> > - int i;
> > + int ret, i;
> >
> > /* Register ourselves with the rest of the world */
> > - if (gic_populate_rdist())
> > - return;
> > + ret = gic_populate_rdist();
> > + if (ret)
> > + return ret;
> >
> > gic_enable_redist(true);
> >
> > @@ -1286,6 +1290,8 @@ static void gic_cpu_init(void)
> >
> > /* initialise system registers */
> > gic_cpu_sys_reg_init();
> > +
> > + return 0;
> > }
> >
> > #ifdef CONFIG_SMP
> > @@ -1295,7 +1301,11 @@ static void gic_cpu_init(void)
> >
> > static int gic_starting_cpu(unsigned int cpu)
> > {
> > - gic_cpu_init();
> > + int ret;
> > +
> > + ret = gic_cpu_init();
> > + if (ret)
> > + return ret;
> >
> > if (gic_dist_supports_lpis())
> > its_cpu_init();
> >
> > But the question is: do you rely on these masks having been
> > "corrected" anywhere else?
> >
> > Thanks,
> >
> > M.
> >
>
>
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