Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get_info()

[Jonathan Cameron]

On Wed, 17 Apr 2024 17:59:36 +0200
"Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote:

> On Wed, Apr 17, 2024 at 5:38 PM Jonathan Cameron
> <Jonathan.Cameron@xxxxxxxxxx> wrote:
> >
> > On Wed, 17 Apr 2024 16:03:51 +0100
> > Salil Mehta <salil.mehta@xxxxxxxxxx> wrote:
> >  
> > > >  From: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> > > >  Sent: Wednesday, April 17, 2024 2:19 PM
> > > >
> > > >  From: James Morse <james.morse@xxxxxxx>
> > > >
> > > >  The arm64 specific arch_register_cpu() call may defer CPU registration until
> > > >  the ACPI interpreter is available and the _STA method can be evaluated.
> > > >
> > > >  If this occurs, then a second attempt is made in acpi_processor_get_info().
> > > >  Note that the arm64 specific call has not yet been added so for now this will
> > > >  be called for the original hotplug case.
> > > >
> > > >  For architectures that do not defer until the ACPI Processor driver loads
> > > >  (e.g. x86), for initially present CPUs there will already be a CPU device. If
> > > >  present do not try to register again.
> > > >
> > > >  Systems can still be booted with 'acpi=off', or not include an ACPI
> > > >  description at all as in these cases arch_register_cpu() will not have
> > > >  deferred registration when first called.
> > > >
> > > >  This moves the CPU register logic back to a subsys_initcall(), while the
> > > >  memory nodes will have been registered earlier.
> > > >  Note this is where the call was prior to the cleanup series so there should be
> > > >  no side effects of moving it back again for this specific case.
> > > >
> > > >  [PATCH 00/21] Initial cleanups for vCPU HP.
> > > >  https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@xxxxxxxxxxxxxxxxxxxxx/
> > > >
> > > >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> > > >
> > > >  Signed-off-by: James Morse <james.morse@xxxxxxx>
> > > >  Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
> > > >  Tested-by: Miguel Luis <miguel.luis@xxxxxxxxxx>
> > > >  Tested-by: Vishnu Pajjuri <vishnu@xxxxxxxxxxxxxxxxxxxxxx>
> > > >  Tested-by: Jianyong Wu <jianyong.wu@xxxxxxx>
> > > >  Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
> > > >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> > > >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> > > >  ---
> > > >  v6: Squash the two paths for conventional CPU Hotplug and arm64
> > > >      vCPU HP.
> > > >  v5: Update commit message to make it clear this is moving the
> > > >      init back to where it was until very recently.
> > > >
> > > >      No longer change the condition in the earlier registration point
> > > >      as that will be handled by the arm64 registration routine
> > > >      deferring until called again here.
> > > >  ---
> > > >   drivers/acpi/acpi_processor.c | 12 +++++++++++-
> > > >   1 file changed, 11 insertions(+), 1 deletion(-)
> > > >
> > > >  diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > >  index 7ecb13775d7f..0cac77961020 100644
> > > >  --- a/drivers/acpi/acpi_processor.c
> > > >  +++ b/drivers/acpi/acpi_processor.c
> > > >  @@ -356,8 +356,18 @@ static int acpi_processor_get_info(struct
> > > >  acpi_device *device)
> > > >      *
> > > >      *  NOTE: Even if the processor has a cpuid, it may not be present
> > > >      *  because cpuid <-> apicid mapping is persistent now.
> > > >  +   *
> > > >  +   *  Note this allows 3 flows, it is up to the arch_register_cpu()
> > > >  +   *  call to reject any that are not supported on a given architecture.
> > > >  +   *  A) CPU becomes present.
> > > >  +   *  B) Previously invalid logical CPU ID (Same as becoming present)
> > > >  +   *  C) CPU already present and now being enabled (and wasn't
> > > >  registered
> > > >  +   *     early on an arch that doesn't defer to here)
> > > >      */
> > > >  -  if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > > >  +  if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> > > >  +       !get_cpu_device(pr->id)) ||
> > > >  +      invalid_logical_cpuid(pr->id) ||
> > > >  +      !cpu_present(pr->id)) {  
> > >
> > >  
> > Hi Salil,
> >
> > Thanks for quick review!
> >  
> > > Logic is clear but it is ugly. We should turn them into macro or inline.  
> >
> > You've found the 'ugly' in this approach vs keeping them separate.
> >
> > For this version I wanted to keep it clear that indeed this condition
> > is a complex mess of different things (and to let people compare
> > it easily with the two paths in v5 to convinced themselves this
> > is the same)
> >
> > It's also a little tricky to do, so will need some thought.
> >
> > I don't think a simple acpi_cpu_is_hotplug() condition is useful
> > as it just moves the complexity away from where a reader is looking
> > and it would only be used in this one case.
> >
> > It doesn't separate well into finer grained subconditions because
> > (C) is a messy case of the vCPU HP case and a not done
> > something else earlier.  The disadvantage of only deferring for
> > arm64 and not other architectures.
> >
> > The best I can quickly come up with is something like this:
> > #define acpi_cpu_not_present(cpu) \
> >         (invalid_logical_cpuid(cpu) || !cpu_present(cpu))
> > #define acpi_cpu_not_enabled(cpu) \
> >         (!invalid_logical_cpuid(cpu) || cpu_present(cpu))
> >
> >         if ((apci_cpu_not_enabled(pr->id) && !get_cpu_device(pr->id) ||
> >             acpi_cpu_not_present(pr->id))
> >
> > Which would still need the same amount of documentation. The
> > code still isn't enough for me to immediately be able to see
> > what is going on.
> >
> > So maybe worth it... I'm not sure.  Rafael, you get to keep this
> > fun, what would you prefer?  
> 
> I would use a static inline function returning bool to carry out these
> checks with comments explaining the different cases in which 'true'
> needs to be returned.

The following makes a subtle logic change (I'll retest tomorrow) but
I think that get_cpu_device(cpu) can never succeed in a path where
hotadd makes sense. 

+/*
+ * Identify if the state transition indicates that hotadd_init
+ * should be called.
+ *
+ * For acpi_processor_add() to be called, the reported state must
+ * now be enabled and present. Conditions reflect prior state.
+ */
+static inline bool acpi_processor_should_hotadd_init(int cpu)
+{
+       /* Already register, initial registration was not deferred */
+       if (get_cpu_device(cpu))
+               return false;
+
+       /* Processor has become present */
+       if (!cpu_present(cpu))
+               return true;
+
+       /* Logical cpuid currently invalid indicates hotadd */
+       if (invalid_logical_cpuid(cpu))
+               return true;
+
+       /*
+        * Previously present and the logical cpu id is valid.
+	 * Deferred registration now _STA can be queries, or
+        * Hotadd due to enabled becoming true on an online capable
+        * CPU.
+        */
+       if (cpu_present(cpu))
+               return true;
+
+       return false;
+}
+
 static int acpi_processor_get_info(struct acpi_device *device)
 {
        union acpi_object object = { 0 };
@@ -356,18 +388,8 @@ static int acpi_processor_get_info(struct acpi_device *device)
         *
         *  NOTE: Even if the processor has a cpuid, it may not be present
         *  because cpuid <-> apicid mapping is persistent now.
-        *
-        *  Note this allows 3 flows, it is up to the arch_register_cpu()
-        *  call to reject any that are not supported on a given architecture.
-        *  A) CPU becomes present.
-        *  B) Previously invalid logical CPU ID (Same as becoming present)
-        *  C) CPU already present and now being enabled (and wasn't registered
-        *     early on an arch that doesn't defer to here)
         */
-       if ((!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
-            !get_cpu_device(pr->id)) ||
-           invalid_logical_cpuid(pr->id) ||
-           !cpu_present(pr->id)) {
+       if (acpi_processor_should_hotadd_init(pr->id)) {
                ret = acpi_processor_hotadd_init(pr, device);