On 01/07/2016 14:44, Radim Krčmář wrote: > 2016-07-01 10:42+0200, Paolo Bonzini: >> On 01/07/2016 00:15, Andrew Honig wrote: >>>>> + /* kvm_apic_map_get_logical_dest() expects multiples of 16 */ >>>>> + size = round_up(max_id + 1, 16); >>> Now that you're using the full range of apic_id values, could this >>> calculation overflow? Perhaps max_id could be u64? >> >> Good point, but I wonder if it's a good idea to let userspace allocate >> 32 GB of memory. :) > > Yes, both could happen. I'll change it to u64 to make it future proof. It's not necessary to change it to u64 if you put a limit, but you can add a WARN_ON(size == 0). Also if kvm_apic_map_get_logical_dest() expects multiples of 16, it should warn whenever the invariant is not respected. >> Let's put a limit on the maximum supported APIC ID, and report it >> through KVM_CHECK_EXTENSION on the new KVM_CAP_X2APIC_API capability. >> If 767 is enough for Knights Landing, the allocation below fits in two >> pages. If you need to make it higher, please change the allocation to >> use kvm_kvzalloc and kvfree. > > We sort of have a capability for maximum APIC ID, KVM_MAX_VCPU_ID, > because VCPU ID is initial APIC ID and x2APIC ID should always be the > initial APIC ID. Should it? According to QEMU if you have e.g. 3 cores per socket one socket take 4 APIC IDs. For Knights Landing the "worst" prime factor in 288 is 3^2 so you need APIC IDs up to 288 * (4/3)^2 = 512. Paolo -- 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
