Message-ID: <20240425105637.000030a7@huawei.com>
Date: Thu, 25 Apr 2024 10:56:37 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Marc Zyngier <maz@...nel.org>, <linuxarm@...wei.com>
CC: Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra
	<peterz@...radead.org>, <linux-pm@...r.kernel.org>,
	<loongarch@...ts.linux.dev>, <linux-acpi@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
	<x86@...nel.org>, Russell King <linux@...linux.org.uk>, "Rafael J . Wysocki"
	<rafael@...nel.org>, Miguel Luis <miguel.luis@...cle.com>, "James Morse"
	<james.morse@....com>, Salil Mehta <salil.mehta@...wei.com>, Jean-Philippe
 Brucker <jean-philippe@...aro.org>, Catalin Marinas
	<catalin.marinas@....com>, Will Deacon <will@...nel.org>, Ingo Molnar
	<mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <justin.he@....com>, <jianyong.wu@....com>
Subject: Re: [PATCH v7 11/16] irqchip/gic-v3: Add support for ACPI's
 disabled but 'online capable' CPUs

On Thu, 25 Apr 2024 10:28:06 +0100
Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:

> On Wed, 24 Apr 2024 13:54:38 +0100
> Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
> 
> > On Tue, 23 Apr 2024 13:01:21 +0100
> > Marc Zyngier <maz@...nel.org> wrote:
> >   
> > > On Mon, 22 Apr 2024 11:40:20 +0100,
> > > Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:    
> > > > 
> > > > On Thu, 18 Apr 2024 14:54:07 +0100
> > > > Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
> > > >       
> > > > > From: James Morse <james.morse@....com>
> > > > > 
> > > > > To support virtual CPU hotplug, ACPI has added an 'online capable' bit
> > > > > to the MADT GICC entries. This indicates a disabled CPU entry may not
> > > > > be possible to online via PSCI until firmware has set enabled bit in
> > > > > _STA.
> > > > > 
> > > > > This means that a "usable" GIC is one that is marked as either enabled,
> > > > > or online capable. Therefore, change acpi_gicc_is_usable() to check both
> > > > > bits. However, we need to change the test in gic_acpi_match_gicc() back
> > > > > to testing just the enabled bit so the count of enabled distributors is
> > > > > correct.
> > > > > 
> > > > > What about the redistributor in the GICC entry? ACPI doesn't want to say.
> > > > > Assume the worst: When a redistributor is described in the GICC entry,
> > > > > but the entry is marked as disabled at boot, assume the redistributor
> > > > > is inaccessible.
> > > > > 
> > > > > The GICv3 driver doesn't support late online of redistributors, so this
> > > > > means the corresponding CPU can't be brought online either. Clear the
> > > > > possible and present bits.
> > > > > 
> > > > > Systems that want CPU hotplug in a VM can ensure their redistributors
> > > > > are always-on, and describe them that way with a GICR entry in the MADT.
> > > > > 
> > > > > When mapping redistributors found via GICC entries, handle the case
> > > > > where the arch code believes the CPU is present and possible, but it
> > > > > does not have an accessible redistributor. Print a warning and clear
> > > > > the present and possible bits.
> > > > > 
> > > > > Signed-off-by: James Morse <james.morse@....com>
> > > > > Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> > > > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>      
> > > > 
> > > > +CC Marc,
> > > > 
> > > > Whilst this has been unchanged for a long time, I'm not 100% sure
> > > > we've specifically drawn your attention to it before now.
> > > > 
> > > > Jonathan
> > > >       
> > > > > 
> > > > > ---
> > > > > v7: No Change.
> > > > > ---
> > > > >  drivers/irqchip/irq-gic-v3.c | 21 +++++++++++++++++++--
> > > > >  include/linux/acpi.h         |  3 ++-
> > > > >  2 files changed, 21 insertions(+), 3 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > > > > index 10af15f93d4d..66132251c1bb 100644
> > > > > --- a/drivers/irqchip/irq-gic-v3.c
> > > > > +++ b/drivers/irqchip/irq-gic-v3.c
> > > > > @@ -2363,11 +2363,25 @@ gic_acpi_parse_madt_gicc(union acpi_subtable_headers *header,
> > > > >  				(struct acpi_madt_generic_interrupt *)header;
> > > > >  	u32 reg = readl_relaxed(acpi_data.dist_base + GICD_PIDR2) & GIC_PIDR2_ARCH_MASK;
> > > > >  	u32 size = reg == GIC_PIDR2_ARCH_GICv4 ? SZ_64K * 4 : SZ_64K * 2;
> > > > > +	int cpu = get_cpu_for_acpi_id(gicc->uid);
> > > > >  	void __iomem *redist_base;
> > > > >  
> > > > >  	if (!acpi_gicc_is_usable(gicc))
> > > > >  		return 0;
> > > > >  
> > > > > +	/*
> > > > > +	 * 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.
> > 
> > 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.
> > 
> > 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?  
> 
> Hi Marc
> 
> Some experiments later (faking this on a physical board - I never liked
> CPU 120 anyway!) and using a different mask brings it's own minor pain.
> 
> When all the rest of the CPUs are brought up cpuhp_bringup_mask() is called
> on cpu_present_mask so we need to do a dance in there to use a temporary
> mask with broken cpus removed.  I think it makes sense to cut that out
> at the top of the cpuhp_bringup_mask() pile of actions rather than trying
> to paper over each actual thing that is dying... (looks like an infinite loop
> somewhere but I haven't tracked down where yet).
> 
> I'll spin a patch so you can see what it looks like, but my concern is
> we are just moving the risk from early users of these masks to later cases
> where code assumes cpu_present_mask definitely means they are present.
> That is probably a small set of cases but not nice either.
> 
> Looks like one of those cases where we need to pick the lesser of two evils
> which is probably still the cpu_broken_mask approach.
> 
> On plus side if we decide to go back to the original approach having seen
> that I already have the code :)
> 
> Jonathan
> 

Patch on top of this series.  If no one shouts before I have it ready I'll
roll a v8 with the mask introduction as a new patch and the other changes pushed into
appropriate patches.

From 361b76f36bfb4ff74fdceca7ebf14cfa43cae4a9 Mon Sep 17 00:00:00 2001
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Date: Wed, 24 Apr 2024 17:42:49 +0100
Subject: [PATCH] cpu: Add broken cpu mask to mark CPUs where inconsistent
 firmware means we can't start them.

On ARM64, it is not currently possible to use CPUs where the GICC entry
in ACPI specifies that it is online capable but not enabled. Only
always enabled entries are supported.

Previously if this condition was met, the present and possible cpu masks
were cleared for the relevant cpus.  However, those masks may already
have been used by other code so this is not known to be safe.

An alternative is to use an additional mask (broken) and check that
in the subset of places where these CPUs might be onlined or the
infrastructure to indicate this is possible created.
Specifically in bringup_nonboot_cpus() and in arch_register_cpu().

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
---
 arch/arm64/kernel/smp.c      |  3 +++
 drivers/irqchip/irq-gic-v3.c |  3 +--
 include/linux/cpumask.h      | 19 +++++++++++++++++++
 kernel/cpu.c                 |  8 +++++++-
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index ccb6ad347df9..39cd6a7c40d8 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -513,6 +513,9 @@ int arch_register_cpu(int cpu)
 	    IS_ENABLED(CONFIG_ACPI_HOTPLUG_CPU))
 		return -EPROBE_DEFER;
 
+	if (cpu_broken(cpu)) /* Inconsistent firmware - can't online */
+		return -ENODEV;
+
 #ifdef CONFIG_ACPI_HOTPLUG_CPU
 	/* For now block anything that looks like physical CPU Hotplug */
 	if (invalid_logical_cpuid(cpu) || !cpu_present(cpu)) {
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 66132251c1bb..a0063eb6484d 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -2377,8 +2377,7 @@ gic_acpi_parse_madt_gicc(union acpi_subtable_headers *header,
 	 */
 	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);
+		set_cpu_broken(cpu);
 		return 0;
 	}
 
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 4b202b94c97a..70a93ad8e590 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -96,6 +96,7 @@ static inline void set_nr_cpu_ids(unsigned int nr)
  *     cpu_enabled_mask  - has bit 'cpu' set iff cpu can be brought online
  *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
  *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration
+ *     cpu_broken_mask  - has bit 'cpu' set iff the cpu should never be onlined
  *
  *  If !CONFIG_HOTPLUG_CPU, present == possible, and active == online.
  *
@@ -130,12 +131,14 @@ extern struct cpumask __cpu_enabled_mask;
 extern struct cpumask __cpu_present_mask;
 extern struct cpumask __cpu_active_mask;
 extern struct cpumask __cpu_dying_mask;
+extern struct cpumask __cpu_broken_mask;
 #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
 #define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
 #define cpu_enabled_mask   ((const struct cpumask *)&__cpu_enabled_mask)
 #define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
 #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
 #define cpu_dying_mask    ((const struct cpumask *)&__cpu_dying_mask)
+#define cpu_broken_mask   ((const struct cpumask *)&__cpu_broken_mask)
 
 extern atomic_t __num_online_cpus;
 
@@ -1073,6 +1076,12 @@ set_cpu_dying(unsigned int cpu, bool dying)
 		cpumask_clear_cpu(cpu, &__cpu_dying_mask);
 }
 
+static inline void
+set_cpu_broken(unsigned int cpu)
+{
+	cpumask_set_cpu(cpu, &__cpu_broken_mask);
+}
+
 /**
  * to_cpumask - convert a NR_CPUS bitmap to a struct cpumask *
  * @bitmap: the bitmap
@@ -1159,6 +1168,11 @@ static inline bool cpu_dying(unsigned int cpu)
 	return cpumask_test_cpu(cpu, cpu_dying_mask);
 }
 
+static inline bool cpu_broken(unsigned int cpu)
+{
+	return cpumask_test_cpu(cpu, cpu_broken_mask);
+}
+
 #else
 
 #define num_online_cpus()	1U
@@ -1197,6 +1211,11 @@ static inline bool cpu_dying(unsigned int cpu)
 	return false;
 }
 
+static inline bool cpu_broken(unsigned int cpu)
+{
+	return false;
+}
+
 #endif /* NR_CPUS > 1 */
 
 #define cpu_is_offline(cpu)	unlikely(!cpu_online(cpu))
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 537099bf5d02..f8b73a11869e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1907,12 +1907,15 @@ static inline bool cpuhp_bringup_cpus_parallel(unsigned int ncpus) { return fals
 
 void __init bringup_nonboot_cpus(unsigned int max_cpus)
 {
+	static const struct cpumask tmp_mask __initdata;
+
 	/* Try parallel bringup optimization if enabled */
 	if (cpuhp_bringup_cpus_parallel(max_cpus))
 		return;
 
+	cpumask_andnot(&tmp_mask, cpu_present_mask, cpu_broken_mask);
 	/* Full per CPU serialized bringup */
-	cpuhp_bringup_mask(cpu_present_mask, max_cpus, CPUHP_ONLINE);
+	cpuhp_bringup_mask(&tmp_mask, max_cpus, CPUHP_ONLINE);
 }
 
 #ifdef CONFIG_PM_SLEEP_SMP
@@ -3129,6 +3132,9 @@ EXPORT_SYMBOL(__cpu_active_mask);
 struct cpumask __cpu_dying_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_dying_mask);
 
+struct cpumask __cpu_broken_mask __ro_after_init;
+EXPORT_SYMBOL(__cpu_broken_mask);
+
 atomic_t __num_online_cpus __read_mostly;
 EXPORT_SYMBOL(__num_online_cpus);
 
-- 
2.39.2


> 
> 
> > 
> > Jonathan
> > 
> > 
> > 
> > 
> > 
> > 
> >   
> > > 
> > > Thanks,
> > > 
> > > 	M.
> > >     
> > 
> > 
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel  
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Powered by blists - more mailing lists