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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Tue, 30 Apr 2024 12:47:34 +0200
Message-ID: <CAJZ5v0hsJBmphEg8gjehtmtzt0Q=Rox1B_qBFrxp15nHvb6o5A@mail.gmail.com>
Subject: Re: [PATCH v8 04/16] ACPI: processor: Move checks and availability of
 acpi_processor earlier
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>, Gavin Shan <gshan@redhat.com>, 
	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>, 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>, Marc Zyngier <maz@kernel.org>, Hanjun Guo <guohanjun@huawei.com>, 
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, 
	Dave Hansen <dave.hansen@linux.intel.com>, linuxarm@huawei.com, justin.he@arm.com, 
	jianyong.wu@arm.com, Lorenzo Pieralisi <lpieralisi@kernel.org>, 
	Sudeep Holla <sudeep.holla@arm.com>
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On Tue, Apr 30, 2024 at 12:45=E2=80=AFPM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Tue, 30 Apr 2024 12:17:38 +0200
> "Rafael J. Wysocki" <rafael@kernel.org> wrote:
>
> > On Tue, Apr 30, 2024 at 12:13=E2=80=AFPM Jonathan Cameron
> > <Jonathan.Cameron@huawei.com> wrote:
> > >
> > > On Tue, 30 Apr 2024 10:28:38 +0100
> > > Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:
> > >
> > > > On Tue, 30 Apr 2024 14:17:24 +1000
> > > > Gavin Shan <gshan@redhat.com> wrote:
> > > >
> > > > > On 4/26/24 23:51, Jonathan Cameron wrote:
> > > > > > Make the per_cpu(processors, cpu) entries available earlier so =
that
> > > > > > they are available in arch_register_cpu() as ARM64 will need ac=
cess
> > > > > > to the acpi_handle to distinguish between acpi_processor_add()
> > > > > > and earlier registration attempts (which will fail as _STA cann=
ot
> > > > > > be checked).
> > > > > >
> > > > > > Reorder the remove flow to clear this per_cpu() after
> > > > > > arch_unregister_cpu() has completed, allowing it to be used in
> > > > > > there as well.
> > > > > >
> > > > > > Note that on x86 for the CPU hotplug case, the pr->id prior to
> > > > > > acpi_map_cpu() may be invalid. Thus the per_cpu() structures
> > > > > > must be initialized after that call or after checking the ID
> > > > > > is valid (not hotplug path).
> > > > > >
> > > > > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > > > >
> > > > > > ---
> > > > > > v8: On buggy bios detection when setting per_cpu structures
> > > > > >      do not carry on.
> > > > > >      Fix up the clearing of per cpu structures to remove unwant=
ed
> > > > > >      side effects and ensure an error code isn't use to referen=
ce them.
> > > > > > ---
> > > > > >   drivers/acpi/acpi_processor.c | 79 +++++++++++++++++++++-----=
---------
> > > > > >   1 file changed, 48 insertions(+), 31 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_=
processor.c
> > > > > > index ba0a6f0ac841..3b180e21f325 100644
> > > > > > --- a/drivers/acpi/acpi_processor.c
> > > > > > +++ b/drivers/acpi/acpi_processor.c
> > > > > > @@ -183,8 +183,38 @@ static void __init acpi_pcc_cpufreq_init(v=
oid) {}
> > > > > >   #endif /* CONFIG_X86 */
> > > > > >
> > > > > >   /* Initialization */
> > > > > > +static DEFINE_PER_CPU(void *, processor_device_array);
> > > > > > +
> > > > > > +static bool acpi_processor_set_per_cpu(struct acpi_processor *=
pr,
> > > > > > +                                struct acpi_device *device)
> > > > > > +{
> > > > > > + BUG_ON(pr->id >=3D nr_cpu_ids);
> > > > >
> > > > > One blank line after BUG_ON() if we need to follow original imple=
mentation.
> > > >
> > > > Sure unintentional - I'll put that back.
> > > >
> > > > >
> > > > > > + /*
> > > > > > +  * Buggy BIOS check.
> > > > > > +  * ACPI id of processors can be reported wrongly by the BIOS.
> > > > > > +  * Don't trust it blindly
> > > > > > +  */
> > > > > > + if (per_cpu(processor_device_array, pr->id) !=3D NULL &&
> > > > > > +     per_cpu(processor_device_array, pr->id) !=3D device) {
> > > > > > +         dev_warn(&device->dev,
> > > > > > +                  "BIOS reported wrong ACPI id %d for the proc=
essor\n",
> > > > > > +                  pr->id);
> > > > > > +         /* Give up, but do not abort the namespace scan. */
> > > > >
> > > > > It depends on how the return value is handled by the caller if th=
e namespace
> > > > > is continued to be scanned. The caller can be acpi_processor_hota=
dd_init()
> > > > > and acpi_processor_get_info() after this patch is applied. So I t=
hink this
> > > > > specific comment need to be moved to the caller.
> > > >
> > > > Good point. This gets messy and was an unintended change.
> > > >
> > > > Previously the options were:
> > > > 1) acpi_processor_get_info() failed for other reasons - this code w=
as never called.
> > > > 2) acpi_processor_get_info() succeeded without acpi_processor_hotad=
d_init (non hotplug)
> > > >    this code then ran and would paper over the problem doing a bunc=
h of cleanup under err.
> > > > 3) acpi_processor_get_info() succeeded with acpi_processor_hotadd_i=
nit called.
> > > >    This code then ran and would paper over the problem doing a bunc=
h of cleanup under err.
> > > >
> > > > We should maintain that or argue cleanly against it.
> > > >
> > > > This isn't helped the the fact I have no idea which cases we care a=
bout for that bios
> > > > bug handling.  Do any of those bios's ever do hotplug?  Guess we ha=
ve to try and maintain
> > > > whatever protection this was offering.
> > > >
> > > > Also, the original code leaks data in some paths and I have limited=
 idea
> > > > of whether it is intentional or not. So to tidy the issue up that y=
ou've identified
> > > > I'll need to try and make that code consistent first.
> > > >
> > > > I suspect the only way to do that is going to be to duplicate the a=
llocations we
> > > > 'want' to leak to deal with the bios bug detection.
> > > >
> > > > For example acpi_processor_get_info() failing leaks pr and pr->thro=
ttling.shared_cpu_map
> > > > before this series. After this series we need pr to leak because it=
's used for the detection
> > > > via processor_device_array.
> > > >
> > > > I'll work through this but it's going to be tricky to tell if we ge=
t right.
> > > > Step 1 will be closing the existing leaks and then we will have som=
ething
> > > > consistent to build on.
> > > >
> > > I 'think' that fixing the original leaks makes this all much more str=
aight forward.
> > > That return 0 for acpi_processor_get_info() never made sense as far a=
s I can tell.
> > > The pr isn't used after this point.
> > >
> > > What about something along lines of.
> > >
> > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_proces=
sor.c
> > > index 161c95c9d60a..97cff4492304 100644
> > > --- a/drivers/acpi/acpi_processor.c
> > > +++ b/drivers/acpi/acpi_processor.c
> > > @@ -392,8 +392,10 @@ static int acpi_processor_add(struct acpi_device=
 *device,
> > >         device->driver_data =3D pr;
> > >
> > >         result =3D acpi_processor_get_info(device);
> > > -       if (result) /* Processor is not physically present or unavail=
able */
> > > -               return 0;
> > > +       if (result) { /* Processor is not physically present or unava=
ilable */
> > > +               result =3D 0;
> >
> > As per my previous message (just sent) this should be an error code,
> > as returning 0 from acpi_processor_add() is generally problematic.
> Ok. I'll switch to that, but as a separate precusor patch. Independent of
> the memory leak fixes.

Sure, thank you!