Commit 2483ef05 authored Sep 25, 2018 by Srikar Dronamraju Committed by Michael Ellerman Sep 25, 2018

powerpc/numa: Use associativity if VPHN hcall is successful



Currently associativity is used to lookup node-id even if the
preceding VPHN hcall failed. However this can cause CPU to be made
part of the wrong node, (most likely to be node 0). This is because
VPHN is not enabled on KVM guests.

With 2ea62630 ("powerpc/topology: Get topology for shared processors at
boot"), associativity is used to set to the wrong node. Hence KVM
guest topology is broken.

For example : A 4 node KVM guest before would have reported.

  [root@localhost ~]#  numactl -H
  available: 4 nodes (0-3)
  node 0 cpus: 0 1 2 3
  node 0 size: 1746 MB
  node 0 free: 1604 MB
  node 1 cpus: 4 5 6 7
  node 1 size: 2044 MB
  node 1 free: 1765 MB
  node 2 cpus: 8 9 10 11
  node 2 size: 2044 MB
  node 2 free: 1837 MB
  node 3 cpus: 12 13 14 15
  node 3 size: 2044 MB
  node 3 free: 1903 MB
  node distances:
  node   0   1   2   3
    0:  10  40  40  40
    1:  40  10  40  40
    2:  40  40  10  40
    3:  40  40  40  10

Would now report:

  [root@localhost ~]# numactl -H
  available: 4 nodes (0-3)
  node 0 cpus: 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15
  node 0 size: 1746 MB
  node 0 free: 1244 MB
  node 1 cpus:
  node 1 size: 2044 MB
  node 1 free: 2032 MB
  node 2 cpus: 1
  node 2 size: 2044 MB
  node 2 free: 2028 MB
  node 3 cpus:
  node 3 size: 2044 MB
  node 3 free: 2032 MB
  node distances:
  node   0   1   2   3
    0:  10  40  40  40
    1:  40  10  40  40
    2:  40  40  10  40
    3:  40  40  40  10

Fix this by skipping associativity lookup if the VPHN hcall failed.

Fixes: 2ea62630 ("powerpc/topology: Get topology for shared processors at boot")
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent 96dc89d5

arch/powerpc/mm/numa.c

+3 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1204,7 +1204,9 @@ int find_and_online_cpu_nid(int cpu)
	int new_nid;		int new_nid;

	/* Use associativity from first thread for all siblings */		/* Use associativity from first thread for all siblings */
	vphn_get_associativity(cpu, associativity);		if (vphn_get_associativity(cpu, associativity))
			return cpu_to_node(cpu);

	new_nid = associativity_to_nid(associativity);		new_nid = associativity_to_nid(associativity);
	if (new_nid < 0 \|\| !node_possible(new_nid))		if (new_nid < 0 \|\| !node_possible(new_nid))
	new_nid = first_online_node;		new_nid = first_online_node;

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