linux-kernel - [PATCH v3] ACPI/PPTT: Check total CPU numbers when a CPU can't be found in PPTT table

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Message-Id: <20260116072943.26322-1-feng.tang@linux.alibaba.com>
Date: Fri, 16 Jan 2026 15:29:43 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Jeremy Linton <jeremy.linton@....com>,
	Hanjun Guo <guohanjun@...wei.com>,
	James Morse <james.morse@....com>
Cc: Joanthan Cameron <Jonathan.Cameron@...wei.com>,
	linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Feng Tang <feng.tang@...ux.alibaba.com>
Subject: [PATCH v3] ACPI/PPTT: Check total CPU numbers when a CPU can't be found in PPTT table

There was a bug that kernel printed error message:
" ACPI PPTT: PPTT table found, but unable to locate core 1 (1)"
and later on the kernel met issues when building up scheduler domain.

Debug showed the kernel actually brought up all 8 CPUs successfully
(MADT and other table worked fine), while the PPTT table was broken
as it only had 4 CPUs in total.

Add check for number of CPU of PPTT table against system CPU number,
and warn if they are not equal, to help debugging similar issues.

Suggested-by: Sudeep Holla <sudeep.holla@....com>
Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>
---
Changelog:

  v3
  * Only check the number of CPUs in PPTT table againt system
    CPU count when error happens, instead of dump all the CPU/cache
	entries (Sudeep/Rafael)

  v2
  * rebase againt 6.19 and refine the commit log

 drivers/acpi/pptt.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index de5f8c018333..9958c3961001 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -529,6 +529,43 @@ static void acpi_pptt_warn_missing(void)
 	pr_warn_once("No PPTT table found, CPU and cache topology may be inaccurate\n");
 }
 
+static void pptt_verify_cpu_count(struct acpi_table_header *table_hdr)
+{
+	struct acpi_subtable_header *entry;
+	unsigned long end;
+	struct acpi_pptt_processor *cpu;
+	u8 len;
+	int nr_pptt_cpus = 0;
+	static bool checked;
+
+	if (checked)
+		return;
+
+	end = (unsigned long)table_hdr + table_hdr->length;
+	entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
+				sizeof(struct acpi_table_pptt));
+
+	while ((unsigned long)entry + sizeof(struct acpi_pptt_processor) <= end) {
+		len = entry->length;
+		if (!len) {
+			pr_warn("Invalid zero length subtable\n");
+			return;
+		}
+
+		cpu = (struct acpi_pptt_processor *)entry;
+		entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry, len);
+		if (cpu->header.type == ACPI_PPTT_TYPE_PROCESSOR &&
+		    (cpu->flags & ACPI_PPTT_ACPI_LEAF_NODE))
+			nr_pptt_cpus++;
+	}
+
+	if (nr_pptt_cpus != num_possible_cpus())
+		pr_warn("The number of CPUs (%d) in PPTT table doesn't match system's CPU count (%d)!\n",
+			nr_pptt_cpus, num_possible_cpus());
+
+	checked = true;
+}
+
 /**
  * topology_get_acpi_cpu_tag() - Find a unique topology value for a feature
  * @table: Pointer to the head of the PPTT table
@@ -565,6 +602,9 @@ static int topology_get_acpi_cpu_tag(struct acpi_table_header *table,
 	}
 	pr_warn_once("PPTT table found, but unable to locate core %d (%d)\n",
 		    cpu, acpi_cpu_id);
+
+	/* Check whether PPTT table's CPU count match with system count */
+	pptt_verify_cpu_count(table);
 	return -ENOENT;
 }
 
-- 
2.39.5 (Apple Git-154)