Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: > 2014-11-27 21:53+0200, Nadav Amit: >> Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: >>> - new->cid_mask = (1 << KVM_X2APIC_CID_BITS) - 1; >>> - new->lid_mask = 0xffff; >>> + new->cid_mask = new->lid_mask = 0xffff; >> You set cid_mask to 0xffff, while there are only 16 clusters. I think it is >> risky (if you twist my hand would come with a scenario). > > Let's see :) APIC id is 8 bit, and we compute cluster part of LDR by > taking four upper bits, so 16 is enough. To clarify my concern - I am worried that some of the CPUs are still in xAPIC mode with LDR that does not follow x2APIC LDR scheme. > It isn't the safest programming practice, but we already fail to check > physical_map bounds and any boost to maximal APIC ID is going to require > a rewrite, thus I didn't bother to do it ... > > All uses should be covered with the following hunk, I will add it to v2 > after all reviews, > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 6c2b8a5..30e4cc1 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -198,7 +198,7 @@ static void recalculate_apic_map(struct kvm *kvm) > cid = apic_cluster_id(new, ldr); > lid = apic_logical_id(new, ldr); > > - if (lid) > + if (lid && cid < ARRAY_SIZE(map->logical_map)) > new->logical_map[cid][ffs(lid) - 1] = apic; > } > out: > > >> Yet, why not to set >> cid_mask to (ARRAY_SIZE(map->logical_map) - 1) ? > > We would incorrectly deliver messages intended for high clusters, > it has to be 0xffff. >From the SDM, I am not sure you are correct, but your solution is fine. Nadav -- 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
