ACPI: CPPC: Fix NULL pointer dereference when nosmp is used

With nosmp in cmdline, other CPUs are not brought up, leaving
their cpc_desc_ptr NULL. CPU0's iteration via for_each_possible_cpu()
dereferences these NULL pointers, causing panic.

Panic backtrace:

[    0.401123] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000b8
...
[    0.403255] [<ffffffff809a5818>] cppc_allow_fast_switch+0x6a/0xd4
...
Kernel panic - not syncing: Attempted to kill init!

Fixes: 3cc30dd00a58 ("cpufreq: CPPC: Enable fast_switch")
Reported-by: Xu Lu <luxu.kernel@bytedance.com>
Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
Link: https://patch.msgid.link/20250604023036.99553-1-cuiyunhui@bytedance.com
[ rjw: New subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index a9ae2fd628630de691f246d9878e49a56c14f2de..6b649031808f805b2bf4212d2ffca6719013d098 100644 (file)
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -476,7 +476,7 @@ bool cppc_allow_fast_switch(void)
        struct cpc_desc *cpc_ptr;
        int cpu;
 
-       for_each_possible_cpu(cpu) {
+       for_each_present_cpu(cpu) {
                cpc_ptr = per_cpu(cpc_desc_ptr, cpu);
                desired_reg = &cpc_ptr->cpc_regs[DESIRED_PERF];
                if (!CPC_IN_SYSTEM_MEMORY(desired_reg) &&