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A concurrent resctrl mount could invoke > intel_pmt_get_regions_by_feature(), acquire the lock, and cache pointers to > the MMIO resources of the devices currently being removed. > When pmt_telem_remove() resumes and re-acquires the lock, it unmaps those > regions. Won't the concurrent reader be left with validly cached but unmapped > memory pointers, leading to a kernel panic when dereferenced by AET? > > This is an existing issue in the pmt_telemetry driver. Scenario is a > race between a resctrl mount and an unbind of a device. The unbind gets > to pmt_telem_remove() but loses the race to acquire ep_lock to the mount > code calling intel_pmt_get_regions_by_feature(). All devices report > valid MMIO addresses and ep_lock is released then pmt_telem_remove() > invalidates the MMIO mappings for the device being unbound/removed. > > Perhaps the telemetry driver should prevent removal of devices for the > interval from intel_pmt_get_regions_by_feature() to intel_pmt_put_feature_group()? > > Can it do that? It looks like I can avoid making this worse if I add a new log "aet_mmio"lock" and use that to protect against invalidation of the MMIO virtual pointers. Then I don't need to drop and reacquire ep_lock. -Tony