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Is it still illegal for TTM? Or there is a possibility for > a race condition here? > Well the question is why does KVM grab the page reference in the first place? If that is to prevent the mapping from changing then yes that's illegal and won't work. It can always happen that you grab the address, solve the fault and then immediately fault again because the address you just grabbed is invalidated. If it's for some other reason than we should probably investigate if we shouldn't stop doing this. Regards, Christian.