On 12/07/2016 22:09, Radim Krčmář wrote: > @@ -619,14 +619,17 @@ static bool kvm_apic_match_logical_addr(struct > kvm_lapic *apic, u32 mda) > /* KVM APIC implementation has two quirks > * - dest always begins at 0 while xAPIC MDA has offset 24, > * - IOxAPIC messages have to be delivered (directly) to x2APIC. > + * > + * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API.
--verbose version: /* KVM APIC implementation has two quirks - * - dest always begins at 0 while xAPIC MDA has offset 24, - * - IOxAPIC messages have to be delivered (directly) to x2APIC. + * - dest always begins at 0 while xAPIC MDA has offset 24. This is + * just a quirk in the API and is not problematic. * - * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. + * - in-kernel IOAPIC messages have to be delivered directly to + * x2APIC, because the kernel does not support interrupt remapping. + * In order to support broadcast without interrupt remapping, x2APIC + * rewrites the destination of non-IPI messages (and also of IPIs sent + * from xAPIC-mode LAPICs) from APIC_BROADCAST to X2APIC_BROADCAST. + * + * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. This is + * important when userspace wants to use x2APIC-format MSIs, because + * APIC_BROADCAST (0xff) is a legal route for "cluster 0, CPUs 0-7". */ Sounds good? Paolo
