Re: [PATCH v9 12/19] arm64: acpi: Harden get_cpu_for_acpi_id() against missing CPU entry

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On 5/1/24 00:24, Jonathan Cameron wrote:
In a review discussion of the changes to support vCPU hotplug where
a check was added on the GICC being enabled if was was online, it was
                                                 ^^^^^^^

                                                 typo

noted that there is need to map back to the cpu and use that to index
into a cpumask. As such, a valid ID is needed.

If an MPIDR check fails in acpi_map_gic_cpu_interface() it is possible
for the entry in cpu_madt_gicc[cpu] == NULL.  This function would
then cause a NULL pointer dereference.   Whilst a path to trigger
this has not been established, harden this caller against the
possibility.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
---
v9: New patch in response to a question from Marc Zyngier.
     Taking the easy way out - harden against a possible condition rather
     than establishing it never happens!
---
  arch/arm64/include/asm/acpi.h | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)


With the typo corrected:

Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>

diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
index bc9a6656fc0c..a407f9cd549e 100644
--- a/arch/arm64/include/asm/acpi.h
+++ b/arch/arm64/include/asm/acpi.h
@@ -124,7 +124,8 @@ static inline int get_cpu_for_acpi_id(u32 uid)
  	int cpu;
for (cpu = 0; cpu < nr_cpu_ids; cpu++)
-		if (uid == get_acpi_id_for_cpu(cpu))
+		if (acpi_cpu_get_madt_gicc(cpu) &&
+		    uid == get_acpi_id_for_cpu(cpu))
  			return cpu;
return -EINVAL;





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