Re: [PATCH] x86/platform/uv: Use alternate source for socket to node data

[Dave Hansen]

On 9/5/23 08:01, Steve Wahl wrote:
> On Fri, Sep 01, 2023 at 02:01:52PM -0500, Steve Wahl wrote:
>> On Fri, Sep 01, 2023 at 10:18:20AM -0700, Dave Hansen wrote:
>>> On 8/7/23 07:17, Steve Wahl wrote:
>>>> When nr_cpus is set to a smaller number than actually present, the
>>>> cpu_to_node() mapping information for unused CPUs is not available to
>>>> build_socket_tables().  This results in an incomplete table and will
>>>> later cause use of a -1 value for some array indexing, and eventual
>>>> kernel page faults.
>>>>
>>>> Switch to using the __apicid_to_node array, which still contains all
>>>> the information mapping apicids to nodes, even for CPUs disabled with
>>>> a reduced nr_cpus setting.
>>> Before, the lookup went:
>>>
>>> 	CPU => APICID => SOCKET
>>>
>>> But when the CPU wasn't present, there wasn't a way to start this lookup.
>>>
>>> So, instead of looping over all CPUs, looking up their APICIDs and
>>> mapping those to sockets, just take CPUs out of the equation entirely.
>>>
>>> Loop over all APICIDs which are mapped to a valid NUMA node.  Then just
>>> extract the socket-id from the APICID.
>>>
>>> Right?
>>>
>>> That seems sane enough.  It's also way less code than the previous approach.
>> Yes.  That's it precisely.  And, yes, way less code.
> Are you willling to give a "Reviewed-by:"?

Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Does this need a stable@ tag when it gets applied?