Re: [PATCH v2] x86/amd_node: Fix PCI device reference counting in amd_smn_init()

[Serge Hallyn <sergeh@kernel.org>]

On Thu, Sep 10, 2026 at 08:03:03PM -0700, Borislav Petkov wrote:
> On Thu, Sep 03, 2026 at 02:37:08PM -0500, Serge Hallyn (AMD) wrote:
> > On Thu, Sep 03, 2026 at 10:43:25AM -0500, Yazen Ghannam wrote:
> > > The local "root" pointer is a temporary variable used during the device
> > > search. Therefore, refcount related to the search iterators should be
> > > cleaned up after the search is complete.
> 
> Ontop of this:
> 
> From: "Borislav Petkov (AMD)" <bp@alien8.de>
> Date: Thu, 10 Sep 2026 18:43:33 -0700
> Subject: [PATCH] x86/topo: Initialize AMD nodes per package
> 
> Sashiko reports that
> 
>   If amd_num_nodes() evaluates to 0, kzalloc_objs(*amd_roots, 0) returns the
>   truthy ZERO_SIZE_PTR (typically (void *)16).
> 
>   Because ZERO_SIZE_PTR is not NULL, the subsequent check for !amd_roots will
>   fail to catch it, resulting in a divide-by-zero kernel panic on the very
>   next line during the __init boot phase.
> 
> Make sure topology_amd_nodes_per_pkg() doesn't return 0 - the AMD nodes per
> package count can be trivially 1 if detection fails just like the rest
> of the max* and num* packages topology attributes.

May not be worth it, but should we also add a num_nodes == 0 or
ZERO_OR_NULL_PTR(amd_roots) check, in case as code churns we
end up with another way for amd_num_nodes() to return 0?

> Closes: https://sashiko.dev/#/patchset/20260903154325.74343-1-yazen.ghannam%40amd.com
> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
> ---
>  arch/x86/kernel/cpu/topology_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
> index 6845e3c63fbb..7a7442981594 100644
> --- a/arch/x86/kernel/cpu/topology_common.c
> +++ b/arch/x86/kernel/cpu/topology_common.c
> @@ -14,7 +14,7 @@
>  struct x86_topology_system x86_topo_system __ro_after_init;
>  EXPORT_SYMBOL_GPL(x86_topo_system);
>  
> -unsigned int __amd_nodes_per_pkg __ro_after_init;
> +unsigned int __amd_nodes_per_pkg __ro_after_init = 1;
>  EXPORT_SYMBOL_GPL(__amd_nodes_per_pkg);
>  
>  /* CPUs which are the primary SMT threads */
> -- 
> 2.53.0
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette