* Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> wrote: > Hrm, would it be possible to save the c2 register upon nmi handler > entry and restore it before iret instead ? This would ensure a > nmi-interrupted page fault handler would continue what it was > doing with a non-corrupted cr2 register after returning from nmi. > > Plus, this involves no modification to the page fault handler fast > path. I guess this kind of nesting would work too - assuming the cr2 can be written to robustly. And i suspect CPU makers pull off a few tricks to stage the cr2 info away from the page fault entry execution asynchronously, so i'd not be surprised if writing to it uncovered unknown-so-far side-effects in CPU implementations. If possible i wouldnt want to rely on such a narrowly possible hack really - any small change in CPU specs could cause problems years down the line. The GUP based method is pretty generic though - and can be used on other architectures as well. It's not as fast as direct access though. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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