[PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map

Radim Krčmář
2016-06-30T20:55:43Z

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 <rkrcmar@redhat.com>
---
v1: use round_up [Peter]

arch/x86/include/asm/kvm_host.h | 9 +++--
arch/x86/kvm/lapic.c | 86 ++++++++++++++++++++++-------------------
arch/x86/kvm/lapic.h | 2 +-
3 files changed, 53 insertions(+), 44 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 53d39771842b..459a789cb3da 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -682,9 +682,12 @@ struct kvm_arch_memory_slot {
struct kvm_apic_map {
struct rcu_head rcu;
u8 mode;
- struct kvm_lapic *phys_map[256];
- /* first index is cluster id second is cpu id in a cluster */
- struct kvm_lapic *logical_map[16][16];
+ u32 size;
+ 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 238b87b068db..eed5af46e619 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -115,26 +115,31 @@ static inline int apic_enabled(struct kvm_lapic *apic)
(LVT_MASK | APIC_MODE_MASK | APIC_INPUT_POLARITY | \
APIC_LVT_REMOTE_IRR | APIC_LVT_LEVEL_TRIGGER)

-/* The logical map is definitely wrong if we have multiple
- * modes at the same time. (Physical map is always right.)
- */
-static inline bool kvm_apic_logical_map_valid(struct kvm_apic_map *map)
-{
- return !(map->mode & (map->mode - 1));
-}
+static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
+ u32 dest_id, struct kvm_lapic ***cluster, u16 *mask) {
+ switch (map->mode) {
+ case KVM_APIC_MODE_X2APIC: {
+ u32 offset = (dest_id >> 16) * 16;
+ if (offset < map->size) {
+ *cluster = &map->phys_map[offset];
+ *mask = dest_id & 0xffff;
+ } else
+ *mask = 0;

-static inline void
-apic_logical_id(struct kvm_apic_map *map, u32 dest_id, u16 *cid, u16 *lid)
-{
- unsigned lid_bits;
-
- BUILD_BUG_ON(KVM_APIC_MODE_XAPIC_CLUSTER != 4);
- BUILD_BUG_ON(KVM_APIC_MODE_XAPIC_FLAT != 8);
- BUILD_BUG_ON(KVM_APIC_MODE_X2APIC != 16);
- lid_bits = map->mode;
-
- *cid = dest_id >> lid_bits;
- *lid = dest_id & ((1 << lid_bits) - 1);
+ return true;
+ }
+ case KVM_APIC_MODE_XAPIC_FLAT:
+ *cluster = map->xapic_flat_map;
+ *mask = dest_id & 0xff;
+ return true;
+ case KVM_APIC_MODE_XAPIC_CLUSTER:
+ *cluster = map->xapic_cluster_map[dest_id >> 4];
+ *mask = dest_id & 0xf;
+ return true;
+ default:
+ /* Not optimized. */
+ return false;
+ }
}

static void recalculate_apic_map(struct kvm *kvm)
@@ -142,17 +147,28 @@ 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 size, 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));
+
+ /* kvm_apic_map_get_logical_dest() expects multiples of 16 */
+ size = round_up(max_id + 1, 16);
+ new = kzalloc(sizeof(struct kvm_apic_map) +
+ sizeof(struct kvm_lapic) * size, GFP_KERNEL);
+
if (!new)
goto out;

+ new->size = size;
+
kvm_for_each_vcpu(i, vcpu, kvm) {
struct kvm_lapic *apic = vcpu->arch.apic;
- u16 cid, lid;
+ struct kvm_lapic **cluster;
+ u16 mask;
u32 ldr, aid;

if (!kvm_apic_present(vcpu))
@@ -161,7 +177,7 @@ 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 < size)
new->phys_map[aid] = apic;

if (apic_x2apic_mode(apic)) {
@@ -174,13 +190,11 @@ static void recalculate_apic_map(struct kvm *kvm)
new->mode |= KVM_APIC_MODE_XAPIC_CLUSTER;
}

- if (!kvm_apic_logical_map_valid(new))
+ if (!kvm_apic_map_get_logical_dest(new, ldr, &cluster, &mask))
continue;

- apic_logical_id(new, ldr, &cid, &lid);
-
- if (lid && cid < ARRAY_SIZE(new->logical_map))
- new->logical_map[cid][ffs(lid) - 1] = apic;
+ if (mask)
+ cluster[ffs(mask) - 1] = apic;
}
out:
old = rcu_dereference_protected(kvm->arch.apic_map,
@@ -684,7 +698,6 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm, struct kvm_lapic
{
int i, lowest;
bool x2apic_ipi;
- u16 cid;

if (irq->shorthand == APIC_DEST_SELF) {
*dst = &src;
@@ -701,7 +714,7 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm, struct kvm_lapic
return false;

if (irq->dest_mode == APIC_DEST_PHYSICAL) {
- if (irq->dest_id >= ARRAY_SIZE(map->phys_map)) {
+ if (irq->dest_id >= map->size) {
*bitmap = 0;
} else {
*dst = &map->phys_map[irq->dest_id];
@@ -710,18 +723,11 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm, struct kvm_lapic
return true;
}

- if (!kvm_apic_logical_map_valid(map))
+ *bitmap = 0;
+ if (!kvm_apic_map_get_logical_dest(map, irq->dest_id, dst,
+ (u16 *)bitmap))
return false;

- apic_logical_id(map, irq->dest_id, &cid, (u16 *)bitmap);
-
- if (cid >= ARRAY_SIZE(map->logical_map)) {
- *bitmap = 0;
- return true;
- }
-
- *dst = map->logical_map[cid];
-
if (!kvm_lowest_prio_delivery(irq))
return true;

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