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Subject[PATCH AUTOSEL 4.18 5/8] powerpc/numa: Use associativity if VPHN hcall is successful
Date
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

[ Upstream commit 2483ef056f6e42f61cd266452e2841165dfe1b5c ]

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 2ea6263 ("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: 2ea626306810 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/mm/numa.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index d531cbdcba6c..055b211b7126 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1204,7 +1204,9 @@ int find_and_online_cpu_nid(int cpu)
int new_nid;

/* 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);
if (new_nid < 0 || !node_possible(new_nid))
new_nid = first_online_node;
--
2.17.1
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