Received-SPF: pass (google.com: domain of linux-kernel+bounces-148975-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Wed, 17 Apr 2024 18:09:39 +0100
From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
CC: Salil Mehta <salil.mehta@huawei.com>, Thomas Gleixner
	<tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"loongarch@lists.linux.dev" <loongarch@lists.linux.dev>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>, "kvmarm@lists.linux.dev"
	<kvmarm@lists.linux.dev>, "x86@kernel.org" <x86@kernel.org>, Russell King
	<linux@armlinux.org.uk>, Miguel Luis <miguel.luis@oracle.com>, James Morse
	<james.morse@arm.com>, Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Dave Hansen
	<dave.hansen@linux.intel.com>, Linuxarm <linuxarm@huawei.com>,
	"justin.he@arm.com" <justin.he@arm.com>, "jianyong.wu@arm.com"
	<jianyong.wu@arm.com>
Subject: Re: [PATCH v6 06/16] ACPI: processor: Register deferred CPUs from
 acpi_processor_get_info()
Message-ID: <20240417180939.00003db7@huawei.com>
In-Reply-To: <CAJZ5v0gJL0mucnN9Na2pCg0ckcTO8cNtpnAcnPD5w9eavUMQcg@mail.gmail.com>
References: <20240417131909.7925-1-Jonathan.Cameron@huawei.com>
	<20240417131909.7925-7-Jonathan.Cameron@huawei.com>
	<22ace9b108ee488eb017f5b3e8facb8d@huawei.com>
	<20240417163842.0000415e@Huawei.com>
	<CAJZ5v0gJL0mucnN9Na2pCg0ckcTO8cNtpnAcnPD5w9eavUMQcg@mail.gmail.com>
Organization: Huawei Technologies R&D (UK) Ltd.
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

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

> On Wed, Apr 17, 2024 at 5:38=E2=80=AFPM Jonathan Cameron
> <Jonathan.Cameron@huawei.com> wrote:
> >
> > On Wed, 17 Apr 2024 16:03:51 +0100
> > Salil Mehta <salil.mehta@huawei.com> wrote:
> > =20
> > > >  From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > > >  Sent: Wednesday, April 17, 2024 2:19 PM
> > > >
> > > >  From: James Morse <james.morse@arm.com>
> > > >
> > > >  The arm64 specific arch_register_cpu() call may defer CPU registra=
tion until
> > > >  the ACPI interpreter is available and the _STA method can be evalu=
ated.
> > > >
> > > >  If this occurs, then a second attempt is made in acpi_processor_ge=
t_info().
> > > >  Note that the arm64 specific call has not yet been added so for no=
w this will
> > > >  be called for the original hotplug case.
> > > >
> > > >  For architectures that do not defer until the ACPI Processor drive=
r 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=3Doff', or not include an A=
CPI
> > > >  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(), whi=
le the
> > > >  memory nodes will have been registered earlier.
> > > >  Note this is where the call was prior to the cleanup series so the=
re 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@shell.armlinux.org.=
uk/
> > > >
> > > >  e.g. 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVIC=
ES")
> > > >
> > > >  Signed-off-by: James Morse <james.morse@arm.com>
> > > >  Reviewed-by: Gavin Shan <gshan@redhat.com>
> > > >  Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > > >  Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > > >  Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > > >  Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > >  Co-developed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > >  Signed-off-by: Joanthan Cameron <Jonathan.Cameron@huawei.com>
> > > >  ---
> > > >  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 poi=
nt
> > > >      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_pro=
cessor.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 pres=
ent
> > > >      *  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 archit=
ecture.
> > > >  +   *  A) CPU becomes present.
> > > >  +   *  B) Previously invalid logical CPU ID (Same as becoming pres=
ent)
> > > >  +   *  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)) { =20
> > >
> > > =20
> > Hi Salil,
> >
> > Thanks for quick review!
> > =20
> > > Logic is clear but it is ugly. We should turn them into macro or inli=
ne. =20
> >
> > 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? =20
>=20
> 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.=20

+/*
+ * 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 =3D { 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 architectu=
re.
-        *  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 regist=
ered
-        *     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 =3D acpi_processor_hotadd_init(pr, device);