Re: [RFC][PATCH 5/6] x86/topo: Fix SNC topology mess

["Chen, Yu C" <yu.c.chen@intel.com>]

On 2/28/2026 3:23 AM, Tim Chen wrote:
> On Fri, 2026-02-27 at 14:01 +0100, Peter Zijlstra wrote:
>> On Thu, Feb 26, 2026 at 11:00:38AM -0800, Tim Chen wrote:
>>> May be a good idea to sanity check that the nodes in the first unit cluster
>>> has the same package id and give a WARNING if that's not the case.
>>
>> But then we'd also have check the second cluster is another package. And
>> if we're checking that, we might as well check they're symmetric.
>>
>> Is this sufficiently paranoid for you? :-)
>>
> 
> Thanks. Looks pretty good and hopefully those warnings will
> never be triggered.
> 
>> +
>> +/* If you NUMA_EMU on top of SNC, you get to keep the pieces */
>> +static void slit_validate(void)
>> +{
>> +	u32 pkg1 = slit_cluster_package(0);
>> +	u32 pkg2 = slit_cluster_package(__num_nodes_per_package);
>> +	WARN_ON(pkg1 == ~0 || pkg2 == ~0 || pkg1 == pkg2);
>> +
>> +	WARN_ON(!slit_cluster_symmetric(0));
>> +	WARN_ON(!slit_cluster_symmetric(__num_nodes_per_package));
>> +}
>> +

Here we check packages0 and 1, should we check all the packages?

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 8735f1968b00..91bac3e2e7fd 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -543,12 +543,13 @@ static u32 slit_cluster_package(int N)
  /* If you NUMA_EMU on top of SNC, you get to keep the pieces */
  static void slit_validate(void)
  {
-       u32 pkg1 = slit_cluster_package(0);
-       u32 pkg2 = slit_cluster_package(__num_nodes_per_package);
-       WARN_ON(pkg1 == ~0 || pkg2 == ~0 || pkg1 == pkg2);
+       for (int pkg = 0; pkg < topology_max_packages(); pkg++) {
+               int node = pkg * __num_nodes_per_package;
+               u32 pkg_id = slit_cluster_package(node);

-       WARN_ON(!slit_cluster_symmetric(0));
-       WARN_ON(!slit_cluster_symmetric(__num_nodes_per_package));
+               WARN_ON(pkg_id == ~0);
+               WARN_ON(!slit_cluster_symmetric(node));
+       }
  }