[PATCH 2/8] nitro_enclaves: Initialise the CPU pool mutex statically

[Alexander Graf <graf@amazon.com>]

ne_cpus is registered with module_param_cb(), so its setter runs while
the parameter section is parsed: from the kernel command line as
nitro_enclaves.ne_cpus= for a built-in driver, or from modprobe
nitro_enclaves ne_cpus=<cpu-list>. parse_args() precedes do_initcalls()
in start_kernel() and do_init_module() in load_module(), so the setter
runs before the driver's own code. It reaches ne_teardown_cpu_pool() and
then ne_setup_cpu_pool(), both of which lock ne_cpu_pool.mutex, while
the mutex_init() for that lock sits in ne_init(). An admin who
configures the pool at boot or at module load therefore takes a mutex
that nothing has initialised. Commit ff8a4d3e3a99 ("nitro_enclaves: Add
logic for setting an enclave vCPU") added those two locks; the parameter
and its runtime mutex_init() were already in place.

Under CONFIG_DEBUG_MUTEXES the first acquire trips a
DEBUG_LOCKS_WARN_ON() in kernel/locking/mutex.c, because ->magic is
still NULL rather than the lock's own address, and the splat carries
parse_args() and ne_set_kernel_param() in its backtrace. It is not a
crash: with lock debugging off nothing is reported and the pool comes
up, which is how this survived. A write to
/sys/module/nitro_enclaves/parameters/ne_cpus is not affected: the
initcall has run before user space exists.

So initialise the mutex where the pool is defined and drop the
mutex_init() call, leaving it valid from the moment the parameter
section is parsed.

Fixes: ff8a4d3e3a99 ("nitro_enclaves: Add logic for setting an enclave vCPU")
Assisted-by: Kiro:claude-opus-5
Signed-off-by: Alexander Graf <graf@amazon.com>
---
 drivers/virt/nitro_enclaves/ne_misc_dev.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/virt/nitro_enclaves/ne_misc_dev.c b/drivers/virt/nitro_enclaves/ne_misc_dev.c
index 8222fbe75800..59e1794587e6 100644
--- a/drivers/virt/nitro_enclaves/ne_misc_dev.c
+++ b/drivers/virt/nitro_enclaves/ne_misc_dev.c
@@ -125,7 +125,9 @@ struct ne_cpu_pool {
 	int		numa_node;
 };
 
-static struct ne_cpu_pool ne_cpu_pool;
+static struct ne_cpu_pool ne_cpu_pool = {
+	.mutex = __MUTEX_INITIALIZER(ne_cpu_pool.mutex),
+};
 
 /**
  * struct ne_phys_contig_mem_regions - Contiguous physical memory regions.
@@ -1761,8 +1763,6 @@ static long ne_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 static int __init ne_init(void)
 {
-	mutex_init(&ne_cpu_pool.mutex);
-
 	return pci_register_driver(&ne_pci_driver);
 }
 
-- 
2.47.1