Messages in this thread Patch in this message | | | From | Radim Krčmář <> | Subject | [PATCH v2 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff | Date | Tue, 13 Dec 2016 17:30:01 +0100 |
| |
LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI, but there is no way to uniquely address it using xAPIC.
From many possible options, we chose the one that also works on real hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in xAPIC mode.
KVM intentionally differs from real hardware, because real hardware (Knights Landing) does just "x2apic_id & 0xff" to decide whether to accept the interrupt in xAPIC mode and it can deliver one interrupt to more than one physical destination, e.g. 0x123 to 0x123 and 0x23.
Fixes: 682f732ecf73 ("KVM: x86: bump MAX_VCPUS to 288") Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> --- v2: * Do not add capability [David, Paolo] * Tag it as a fix [David] --- arch/x86/kvm/lapic.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index bc8df7ce2766..f1b22bb76a4a 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -199,10 +199,15 @@ static void recalculate_apic_map(struct kvm *kvm) xapic_id = kvm_xapic_id(apic); x2apic_id = kvm_x2apic_id(apic); - if (apic_x2apic_mode(apic) && + /* Hotplug hack: see kvm_apic_match_physical_addr(), ... */ + if ((apic_x2apic_mode(apic) || x2apic_id > 0xff) && x2apic_id <= new->max_apic_id) new->phys_map[x2apic_id] = apic; - else if (!apic_x2apic_mode(apic)) + /* + * ... xAPIC ID of VCPUs with APIC ID > 0xff will wrap-around, + * prevent them from masking VCPUs with APIC ID <= 0xff. + */ + if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id]) new->phys_map[xapic_id] = apic; ldr = kvm_lapic_get_reg(apic, APIC_LDR); @@ -612,6 +617,10 @@ static bool kvm_apic_match_physical_addr(struct kvm_lapic *apic, u32 mda) if (apic_x2apic_mode(apic)) return mda == kvm_x2apic_id(apic); + /* Hotplug hack: LAPIC in xAPIC mode also accepts x2APIC. */ + if (kvm_x2apic_id(apic) > 0xff && mda == kvm_x2apic_id(apic)) + return true; + return mda == kvm_xapic_id(apic); } -- 2.11.0
| |