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KVM: x86: allow hotplug of VCPU with APIC ID over 0xff 

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: 682f732ecf ("KVM: x86: bump MAX_VCPUS to 288")
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Radim Krčmář 2016-12-15 18:06:48 +01:00
parent b4535b58ae
commit 5bd5db385b
1 changed files with 25 additions and 5 deletions
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30
arch/x86/kvm/lapic.c
View File

@ -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);
}