Re: [PATCH v2 1/2] x86/amd_node: Avoid divide by zero on virtualized systems

Hi,

On 2026-08-14 17:42, Jason Andryuk wrote:
> On a virtualized system, the number of nodes does not have a
> relationship to the number of roots.  A Xen PVH dom0 can calculate
> roots_per_node as 0, which crashes with a divide by zero in:
> 
>      if (count++ % roots_per_node)
> 
> The issue is seen with Xen, but it could affect other systems.
> 
> Change roots_per_node == 0 to 1 to allow the system to boot.  Print a
> warning when this is performed for non-virtualized systems.
> 
> Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
> Cc: [email protected]
> Suggested-by: Borislav Petkov <[email protected]>
> Signed-off-by: Jason Andryuk <[email protected]>

Any feedback here?

Thanks,
Jason

> ---
> v2:
> Print as a warning instead of error
> Use "!" instead of "== 0".
> 
> X86_FEATURE_XENPV is only for PV, but this is observed with a PVH dom0.
> ---
>   arch/x86/kernel/amd_node.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
> index 0be01725a2a4..c3e214925d9c 100644
> --- a/arch/x86/kernel/amd_node.c
> +++ b/arch/x86/kernel/amd_node.c
> @@ -287,6 +287,11 @@ static int __init amd_smn_init(void)
>   		return -ENOMEM;
>   
>   	roots_per_node = num_roots / num_nodes;
> +	if (!roots_per_node) {
> +		if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR))
> +			pr_warn(FW_BUG "Error detecting roots per node.");
> +		roots_per_node = 1;
> +	}
>   
>   	count = 0;
>   	node = 0;