[PATCH v3 04/14] KVM: x86: dynamic kvm_apic_map

[Radim Krčmář]

x2APIC supports up to 2^32-1 LAPICs, but most guest in coming years will
have slighly less VCPUs.  Dynamic size saves memory at the cost of
turning one constant into a variable.

apic_map mutex had to be moved before allocation to avoid races with cpu
hotplug.

Signed-off-by: Radim Krčmář <rkrc...@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |  3 ++-
 arch/x86/kvm/lapic.c            | 18 +++++++++++++-----
 arch/x86/kvm/lapic.h            |  2 +-
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3194b19b9c7b..643e3dffcd85 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -682,11 +682,12 @@ struct kvm_arch_memory_slot {
 struct kvm_apic_map {
        struct rcu_head rcu;
        u8 mode;
-       struct kvm_lapic *phys_map[256];
+       u32 max_apic_id;
        union {
                struct kvm_lapic *xapic_flat_map[8];
                struct kvm_lapic *xapic_cluster_map[16][4];
        };
+       struct kvm_lapic *phys_map[];
 };
 
 /* Hyper-V emulation context */
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 9880d03f533d..224fc1c5fcc6 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -120,7 +120,7 @@ static inline bool kvm_apic_map_get_logical_dest(struct 
kvm_apic_map *map,
        switch (map->mode) {
        case KVM_APIC_MODE_X2APIC: {
                u32 offset = (dest_id >> 16) * 16;
-               u32 max_apic_id = ARRAY_SIZE(map->phys_map) - 1;
+               u32 max_apic_id = map->max_apic_id;
 
                if (offset <= max_apic_id) {
                        u8 cluster_size = min(max_apic_id - offset + 1, 16U);
@@ -152,14 +152,22 @@ static void recalculate_apic_map(struct kvm *kvm)
        struct kvm_apic_map *new, *old = NULL;
        struct kvm_vcpu *vcpu;
        int i;
-
-       new = kzalloc(sizeof(struct kvm_apic_map), GFP_KERNEL);
+       u32 max_id = 255;
 
        mutex_lock(&kvm->arch.apic_map_lock);
 
+       kvm_for_each_vcpu(i, vcpu, kvm)
+               if (kvm_apic_present(vcpu))
+                       max_id = max(max_id, kvm_apic_id(vcpu->arch.apic));
+
+       new = kzalloc(sizeof(struct kvm_apic_map) +
+                     sizeof(struct kvm_lapic *) * (max_id + 1), GFP_KERNEL);
+
        if (!new)
                goto out;
 
+       new->max_apic_id = max_id;
+
        kvm_for_each_vcpu(i, vcpu, kvm) {
                struct kvm_lapic *apic = vcpu->arch.apic;
                struct kvm_lapic **cluster;
@@ -172,7 +180,7 @@ static void recalculate_apic_map(struct kvm *kvm)
                aid = kvm_apic_id(apic);
                ldr = kvm_lapic_get_reg(apic, APIC_LDR);
 
-               if (aid < ARRAY_SIZE(new->phys_map))
+               if (aid <= new->max_apic_id)
                        new->phys_map[aid] = apic;
 
                if (apic_x2apic_mode(apic)) {
@@ -710,7 +718,7 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm 
*kvm,
                return false;
 
        if (irq->dest_mode == APIC_DEST_PHYSICAL) {
-               if (irq->dest_id >= ARRAY_SIZE(map->phys_map)) {
+               if (irq->dest_id > map->max_apic_id) {
                        *bitmap = 0;
                } else {
                        *dst = &map->phys_map[irq->dest_id];
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 336ba51bb16e..8d811139d2b3 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -200,7 +200,7 @@ static inline int kvm_lapic_latched_init(struct kvm_vcpu 
*vcpu)
        return lapic_in_kernel(vcpu) && test_bit(KVM_APIC_INIT, 
&vcpu->arch.apic->pending_events);
 }
 
-static inline int kvm_apic_id(struct kvm_lapic *apic)
+static inline u32 kvm_apic_id(struct kvm_lapic *apic)
 {
        return (kvm_lapic_get_reg(apic, APIC_ID) >> 24) & 0xff;
 }
-- 
2.9.0