2014-08-20 17:34+0200, Paolo Bonzini: > Il 20/08/2014 17:31, Radim Krčmář ha scritto: > > Btw. without extra code, we are still going to overflow on races when > > changing PW_grow, should they be covered as well? > > You mean because there is no spinlock or similar protecting the changes? > I guess you could use a seqlock. Yes, for example between a modification of ple_window new = min(old, PW_actual_max) * PW_grow which gets compiled into something like this: 1) tmp = min(old, PW_actual_max) 2) new = tmp * PW_grow and a write to increase PW_grow 3) PW_actual_max = min(PW_max / new_PW_grow, PW_actual_max) 4) PW_grow = new_PW_grow 5) PW_actual_max = PW_max / new_PW_grow 3 and 4 can exectute between 1 and 2, which could overflow. I don't think they are important enough to warrant a significant performance hit of locking. Or even more checks that would prevent it in a lockless way. (I'd just see that the result is set to something legal and also drop line 3, because it does not help things that much.) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
