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This means the persistent ring buffer, which relies on a >> coherent state of memory, may not have its events written to the buffer >> and they may be lost. Moreover, there may be inconsistency with the >> counters which are used for validation of the integrity of the >> persistent ring buffer which may cause all data to be discarded. >> >> To avoid this issue, stop recording of the ring buffer on panic and >> flush the cache of the ring buffer's memory. > > Hmm, on some architectures, flush_cache_vmap() is implemented using > on_each_cpu() which waits IPI. But that does not safe in panic notifier > because it is called after smp_send_stop(). > > Since this cache flush issue is currently only confirmed on arm64, > I would like to make it doing nothing (do { } while (0)) by default. FWIW, I've sent a related series a while ago about flushing pmem areas to memory on panic: https://lore.kernel.org/lkml/20240618154157.334602-3-mathieu.desnoyers@efficios.com/ When reading your patch, I feel like I'm missing something, so please bear with me for a few questions: - What exactly are you trying to flush ? By "flush" do you mean evince cache lines or write back cache lines ? (I expect you aim at the second option) - AFAIU, you are not trying to evince cache lines after creation of a new virtual mapping (which is the documented intent of flush_cache_vmap). - AFAIU flush_cache_vmap maps to no-code on arm64 (asm-generic), what am I missing ? It makes sense to be a no-op because AFAIR arm64 does not have to deal with virtually aliasing caches. see commit 8690bbcf3b7 ("Introduce cpu_dcache_is_aliasing() across all architectures") The arch_wb_cache_pmem is specific to pmem, which is not exactly what you want to use, but on arm64 it's implemented as: /* Ensure order against any prior non-cacheable writes */ dmb(osh); dcache_clean_pop((unsigned long)addr, (unsigned long)addr + size); Which I think has the writeback semantic you are looking for, and AFAIU should no require IPIs (at least on arm64) to flush cache lines across the entire system. Cheers, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com