Messages in this thread | | | Date | Wed, 20 Aug 2014 18:01:38 +0200 | From | Radim Krčmář <> | Subject | Re: [PATCH 9/9] KVM: VMX: automatic PLE window maximum |
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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 linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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