On Tue, 2023-10-10 at 10:24 +0000, Huang, Kai wrote:
> > /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> > @@ -74,6 +75,9 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> >
> >
> > acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> >
> >
> > + /* Disable CPU onlining/offlining */
> > + cpu_hotplug_not_supported();
> > +
>
> Both onlining/offlining are prevented, or just offlining?
>
> The previous patch says:
>
> It does not prevent the initial bring up of the CPU, but it stops
> subsequent offlining.
>
> And ...
>
> [...]
>
>
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -1522,7 +1522,7 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
> > * If the platform does not support hotplug, report it explicitly to
> > * differentiate it from a transient offlining failure.
> > */
> > - if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) || !cpu_hotplug_supported)
> > + if (!cpu_hotplug_supported)
> > return -EOPNOTSUPP;
> > if (cpu_hotplug_disabled)
> > return -EBUSY;
>
> ... here cpu_down_maps_locked() only prevents offlining if I am reading
> correctly.
>
> Also, can we rename cpu_hotplug_supported to cpu_offline_supported to match the
> behaviour better?
>
> Anyway, isn't it a little bit odd to have:
>
> if (!cpu_hotplug_supported)
> return -EOPNOTSUPP;
> if (cpu_hotplug_disabled)
> return -EBUSY;
>
> ?
I probably have missed something important, but I don't quite understand what's
the reason to have the CC_ATTR_HOTPLUG_DISABLED at the beginning, and now
replace it with cpu_hotplug_not_supported()?
>From the changelog:
Currently hotplug prevented based on the confidential computing
attribute which is set for Intel TDX. But TDX is not the only possible
user of the wake up method.
CC_ATTR_HOTPLUG_DISABLED is only used by TDX guest, but MADT can be used by non-
TDX guest too.
Anyway, if the purpose is just to prevent CPU from going offline, can this be
done by registering a cpuhp callback?
static int madt_wakeup_offline_cpu(unsigned int cpu)
{
return -EOPNOTSUPP;
}
...
err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "madt-wakeup",
NULL, madt_wakeup_offline_cpu);
if (err) {
pr_err("Register CPU hotplug callback failed.\n");
/* BUG() ??? */
}
This doesn't pollute the common CPU hotplug code, thus to me looks more clear?
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