Re: [PATCH 1/2] x86/amd_node: Remove smn_exclusive

[Mario Limonciello <superm1@kernel.org>]

On 8/10/26 09:07, Yazen Ghannam wrote:
> On Thu, Aug 06, 2026 at 12:01:56PM -0400, Jason Andryuk wrote:
>> amd_smn_read/write() are exported functions around __amd_smn_rw(), so
>> they are always available even if amd_smn_init() fails.  smn_exclusive
>> would prevent access __amd_smn_rw(), but it is placed too late.  If
>> amd_smn_init() failed, amd_roots is NULL and __amd_smn_rw() will fault
>> over it.  Replace smn_exclusive with directly checking amd_roots to
>> avoid the NULL pointer dereference.
>>
>> Fixes: 77466b798d59 ("x86/amd_node: Remove dependency on AMD_NB")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
>> ---
>> Fixes is the introduction of amd_roots
>> ---
>>   arch/x86/kernel/amd_node.c | 9 +++------
>>   1 file changed, 3 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
>> index 0be01725a2a4..ea553267e5fa 100644
>> --- a/arch/x86/kernel/amd_node.c
>> +++ b/arch/x86/kernel/amd_node.c
>> @@ -38,7 +38,6 @@ static struct pci_dev **amd_roots;
>>   
>>   /* Protect the PCI config register pairs used for SMN. */
>>   static DEFINE_MUTEX(smn_mutex);
>> -static bool smn_exclusive;
>>   
>>   #define SMN_INDEX_OFFSET	0x60
>>   #define SMN_DATA_OFFSET		0x64
>> @@ -91,11 +90,11 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, b
>>   	if (node >= amd_num_nodes())
>>   		return err;
>>   
>> -	root = amd_roots[node];
>> -	if (!root)
>> +	if (!amd_roots)
>>   		return err;
>>   
>> -	if (!smn_exclusive)
>> +	root = amd_roots[node];
>> +	if (!root)
>>   		return err;
>>   
>>   	guard(mutex)(&smn_mutex);
>> @@ -308,8 +307,6 @@ static int __init amd_smn_init(void)
>>   		debugfs_create_file("value",	0600, debugfs_dir, NULL, &smn_value_fops);
>>   	}
>>   
>> -	smn_exclusive = true;
>> -
>>   	return 0;
>>   }
>>   
> 
> 'smn_exclusive' wasn't originally intended to be used for bounds
> checking the array. But the original use is no longer needed, so it can
> be removed.
> 
> Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
> 
> Thanks,
> Yazen

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>