[PATCH v2] ACPI: CPPC: Add NULL pointer check to cppc_get_perf()

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH] ACPI: CPPC: Add NULL pointer check to cppc_get_perf()

Check cpc_desc against NULL in cppc_get_perf(), so it doesn't crash
down the road if cpc_desc is NULL.

Fixes: 0654cf05d17b ("ACPI: CPPC: Introduce cppc_get_nominal_perf()")
Reported-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 5.15+ <stable@vger.kernel.org> # 5.15+
---

-> v2: Check cpc_desc against NULL before using it to initialize reg.

---
 drivers/acpi/cppc_acpi.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/acpi/cppc_acpi.c
===================================================================
--- linux-pm.orig/drivers/acpi/cppc_acpi.c
+++ linux-pm/drivers/acpi/cppc_acpi.c
@@ -998,7 +998,14 @@ static int cpc_write(int cpu, struct cpc
 static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
 {
 	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
-	struct cpc_register_resource *reg = &cpc_desc->cpc_regs[reg_idx];
+	struct cpc_register_resource *reg;
+
+	if (!cpc_desc) {
+		pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
+		return -ENODEV;
+	}
+
+	reg = &cpc_desc->cpc_regs[reg_idx];
 
 	if (CPC_IN_PCC(reg)) {
 		int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);