From 5bd5db385b3e13c702365574c0b7350c6ea45e84 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Date: Thu, 15 Dec 2016 18:06:48 +0100 Subject: [PATCH] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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") Reviewed-by: David Hildenbrand Signed-off-by: Radim Krčmář Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 3ebef53d20a0..7e9ac4606279 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -189,15 +189,26 @@ static void recalculate_apic_map(struct kvm *kvm) struct kvm_lapic *apic = vcpu->arch.apic; struct kvm_lapic **cluster; u16 mask; - u32 ldr, aid; + u32 ldr; + u8 xapic_id; + u32 x2apic_id; if (!kvm_apic_present(vcpu)) continue; - aid = apic_x2apic_mode(apic) ? kvm_x2apic_id(apic) - : kvm_xapic_id(apic); - if (aid <= new->max_apic_id) - new->phys_map[aid] = apic; + xapic_id = kvm_xapic_id(apic); + x2apic_id = kvm_x2apic_id(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; + /* + * ... 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); @@ -604,6 +615,15 @@ 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: Make LAPIC in xAPIC mode also accept interrupts as if + * it were in x2APIC mode. Hotplugged VCPUs start in xAPIC mode and + * this allows unique addressing of VCPUs with APIC ID over 0xff. + * The 0xff condition is needed because writeable xAPIC ID. + */ + if (kvm_x2apic_id(apic) > 0xff && mda == kvm_x2apic_id(apic)) + return true; + return mda == kvm_xapic_id(apic); } -- 2.20.1