[PATCH v6 11/16] irqchip/gic-v3: Add support for ACPI's disabled but 'online capable' CPUs

Jonathan Cameron
2024-04-17T13:24:50Z

From: James Morse <james.morse@arm.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@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v5: 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;
+ }
+
redist_base = ioremap(gicc->gicr_base_address, size);
if (!redist_base)
return -ENOMEM;
@@ -2413,9 +2427,12 @@ static int __init gic_acpi_match_gicc(union acpi_subtable_headers *header,

/*
* If GICC is enabled and has valid gicr base address, then it means
- * GICR base is presented via GICC
+ * GICR base is presented via GICC. The redistributor is only known to
+ * be accessible if the GICC is marked as enabled. If this bit is not
+ * set, we'd need to add the redistributor at runtime, which isn't
+ * supported.
*/
- if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address)
+ if (gicc->flags & ACPI_MADT_ENABLED && gicc->gicr_base_address)
acpi_data.enabled_rdists++;

return 0;
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 9844a3f9c4e5..fcfb7bb6789e 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -239,7 +239,8 @@ void acpi_table_print_madt_entry (struct acpi_subtable_header *madt);

static inline bool acpi_gicc_is_usable(struct acpi_madt_generic_interrupt *gicc)
{
- return gicc->flags & ACPI_MADT_ENABLED;
+ return gicc->flags & (ACPI_MADT_ENABLED |
+ ACPI_MADT_GICC_ONLINE_CAPABLE);
}

/* the following numa functions are architecture-dependent */
--
2.39.2