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What am I missing? > > I think you're looking at it from the wrong side... (or it is too late > here, but we'll see). Forget how a memory type can be mapped but think > about how the recovery action looks like. > > - DRAM: when a DRAM page is poisoned, it is only poisoned as a whole > page by memory_failure(). whole_page is always true here, no matter what > the hardware says because we don't and cannot do any sub-page recovery > actions. So it doesn't matter how we map it, UC, NP... I suggested NP > because the page is practically not present if you want to access it > because mm won't allow it... > > - PMEM: reportedly, we can do sub-page recovery here so PMEM should be > mapped in the way it is better for the recovery action to work. > > In both cases, the recovery action should control how the memory type is > mapped. > > Now, you say we cannot know the memory type when the error gets > reported. > > And I say: for simplicity's sake, we simply go and work with whole > pages. Always. That is the case anyway for DRAM. Sorry, please correct me if I misunderstand. The DRAM poison handling at page frame granularity is a helpless compromise due to lack of guarantee to decipher the precise error blast radius given all types of DRAM and architectures, right? But that's not true for the PMEM case. So why should PMEM poison handling follow the lead of DRAM? Regards, -jane > > For PMEM, AFAIU, it doesn't matter whether it is a whole page or not - > the PMEM driver knows how to do those sub-pages accesses. > > IOW, set_mce_nospec() should simply do: > > rc = set_memory_np(decoy_addr, 1); > > and that's it. >