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

[Yazen Ghannam]

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@xxxxxxxxxxxxxxx
> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> ---
> 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@xxxxxxx>

Thanks,
Yazen