2013-12-16 13:55+0100, Radim Krčmář: > 2013-12-16 14:16+0200, Gleb Natapov: > > On Mon, Dec 16, 2013 at 01:01:10PM +0100, Radim Krčmář wrote: > > > > > - Where does the 'only one supported cluster' come from? > > > > > > > > > "only one supported cluster" comes from 8 bit cpuid limitation of KVM's x2apic > > > > implementation. With 8 bit cpuid you can only address cluster 0 in logical mode. > > > > > > One x2apic cluster has 16 cpus and we generate the x2apic LDR correctly, > > > so 8 bit cpuid can address first 16 clusters as well. > > > > > > u32 ldr = ((id >> 4) << 16) | (1 << (id & 0xf)); > > > > > Interrupt from a device cannot generate such ldr, only IPI can. Only > > 4 cpus in cluster zero are addressable in clustering mode by a > > device. Without irq remapping x2apic is a PV interface between host > > and guest where guest needs to know KVM implementation's limitation to > > use it. > > Thanks, I'll read more about devices ... still no idea how could they > address cluster > 15. > > > I do not see a point in fixing problems in x2apic logical mode > > emulation right now since it will not make it usable, as long as > > there is not security problems there. > > Agreed; I wanted to know why this patch was correct, if we cared. > > > > > > I only see we use 'struct kvm_lapic *logical_map[16][16];', which > > > > > supports 16 clusters of 16 apics = first 256 vcpus, so if we map > > > > > everything to logical_map[0][0:15], we would not work correctly in > > > > > the cluster x2apic, with > 16 vcpus. > > > > > > > > > Such config cannot work today because of 8 bit cpuid limitation. When the limitation > > > > will be removed KMV_X2APIC_CID_BITS will be set to actual number of bits we want to support. > > > > > > Even with KMV_X2APIC_CID_BITS = 4, which would allow us to support 8 bit > > > cpuid, we would still deliver interrupts destined for cpuid > 256 to > > > potentially plugged cpus. > > Again, KMV_X2APIC_CID_BITS = 4 will not allow us to support 8 bit cpuids > > unfortunately, not sure what you mean by the second part of the sentence. > > Sorry, I meant that with this change, we map all clusters to cluster 0, > which has two flaws: > - in kvm_lapic_set_base(), the order of vcpu creation determines those Gah, should have been 'recalculate_apic_map()' ... The patch would be especially surprising with a dynamic adding of vcpus. > assigned to cluster 0, and the rest is unaddressable (overwritten) > - we can send IPI to an unplugged high cpuid and it arives in cluster 0 > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html