PMU: Placeholder for future poisoned counters mitigation...

[atulkharerivos]

When counters are saved and restored during a vCPU context switch, we might encounter an improbable error while configuring, starting, or stopping a previously functioning counter. Salus handles this case by marking the counter as "poisoned", meaning that its value is permanently frozen until the guest shuts down. It's possible that either migrating the guest to a new platform, or trying to configure the counter once again might alleviate the situation.

Per the chat with @atishp04, it's OK to punt on the issue right now, and revisit in the future.