CA-421274: reset vcpu affinity if node claim failed

[mg12]

When the VM fails to claim pages on a single node:

• Before this change: incorrect: the VM ends up with the memory spread across nodes, but the VCPUs affine to the PCPUs of a single node.
• After this change: correct: the VM ends up with both the memory spread across nodes and the VCPUs affine to the PCPUs of all nodes.

2025-12-11T02:24:19.613750+00:00 genus-34-29d xenopsd-xc: [debug||41 |VM.pool_migrate R:6973ccb34e76|softaffinity] 
Allocated resources: { "affinity" =\x0A   [0; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; \x0A    19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; \x0A    36; 37; 38; 39];\x0A  "cores" = 20;\x0A  "memfree" = 63555600384 }
2025-12-11T02:24:19.613835+00:00 genus-34-29d xenopsd-xc: [ info||41 |VM.pool_migrate R:6973ccb34e76|xenops] 
Domain.numa_placement.(fun): unable to claim enough memory, domain 4 won't be hosted in a single NUMA node. (error Cannot allocate memory)
2025-12-11T02:24:19.613881+00:00 genus-34-29d xenopsd-xc: [debug||41 |VM.pool_migrate R:6973ccb34e76|xenops] 
Domain.numa_placement.(fun).reset_affinity: resetting vcpu affinity for domain 4 to all CPUs: [0; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; \x0A 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; \x0A 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; \x0A 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; \x0A 71; 72; 73; 74; 75; 76; 77; 78; 79]

A debug line is added to verify that the reset of the vcpu affinity occurred as expected.

[lindig]

Almost the same code appears above (calling set_affiniity for all vcpus)

[edwintorok]

would it work to invert the order operations?
instead of setting the affinity, then claiming, then resetting the affinity: can we claim first, and if successful then set the affinity?
(Unless the claiming code in Xen looks at affinity?)

[mg12]

@psafont do you remember if there's any requirement in setting the vcpu affinity before claiming?

[psafont]

I don't think that setting the affinity can fail. Therefore it make sense that the claims are done before setting the affinity.