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But the mapping is >> really percpu, so the mapping to the physical address belonging to >> another CPU should never pollute the current CPU's cache if I don't miss >> something. >> >>> I'm sure code can end up accessing the current cpu's percpu data >>> using the same address that other cpu use - there are definitely >>> places where it needs that address. >> No, it is not. In the percpu page table approach, we use different >> address for this_cpu_*() and per_cpu_ptr() which is mainly used to >> initialize percpu data for all CPUs. > You missed something. > > Look, for example, at kernel/locking/osq_lock.c > The code uses this_cpu_ptr() and then both dereferences the pointer > and writes it to places that other cpu will use. > It also uses per_cpu_ptr() to get an address it can use for the per-cpu > data of another cpu. > (That code all assumes preemption is disabled.) this_cpu_ptr() uses different addresses for different CPUs. It is a special case, it is not due to VIVT, but because it may confuse list API. Because list API determines list is empty by comparing pointers (head->next == head). this_cpu_read/write/add/sub, etc, are fine. And per_cpu_ptr() also uses different addresses for different CPUs. The lwn article explained it. https://lwn.net/SubscriberLink/1073395/12c08f128e515809/ Thanks, Yang > > -- David > >> Thanks, >> Yang