[PATCH v5 18/33] KVM: x86: Explicitly track all possibilities for APIC map's logical modes

Sean Christopherson
2023-01-06T01:15:30Z

Track all possibilities for the optimized APIC map's logical modes
instead of overloading the pseudo-bitmap and treating any "unknown" value
as "invalid".

As documented by the now-stale comment above the mode values, the values
did have meaning when the optimized map was originally added. That
dependent logical was removed by commit e45115b62f9a ("KVM: x86: use
physical LAPIC array for logical x2APIC"), but the obfuscated behavior
and its comment were left behind.

Opportunistically rename "mode" to "logical_mode", partly to make it
clear that the "disabled" case applies only to the logical map, but also
to prove that there is no lurking code that expects "mode" to be a bitmap.

Functionally, this is a glorified nop.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm_host.h | 29 ++++++++++++++++--------
arch/x86/kvm/lapic.c | 40 ++++++++++++++++++++++++++-------
2 files changed, 52 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1d92c148e799..732421a0ad02 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1022,19 +1022,30 @@ struct kvm_arch_memory_slot {
};

/*
- * We use as the mode the number of bits allocated in the LDR for the
- * logical processor ID. It happens that these are all powers of two.
- * This makes it is very easy to detect cases where the APICs are
- * configured for multiple modes; in that case, we cannot use the map and
- * hence cannot use kvm_irq_delivery_to_apic_fast either.
+ * Track the mode of the optimized logical map, as the rules for decoding the
+ * destination vary per mode. Enabling the optimized logical map requires all
+ * software-enabled local APIs to be in the same mode, each addressable APIC to
+ * be mapped to only one MDA, and each MDA to map to at most one APIC.
*/
-#define KVM_APIC_MODE_XAPIC_CLUSTER 4
-#define KVM_APIC_MODE_XAPIC_FLAT 8
-#define KVM_APIC_MODE_X2APIC 16
+enum kvm_apic_logical_mode {
+ /* All local APICs are software disabled. */
+ KVM_APIC_MODE_SW_DISABLED,
+ /* All software enabled local APICs in xAPIC cluster addressing mode. */
+ KVM_APIC_MODE_XAPIC_CLUSTER,
+ /* All software enabled local APICs in xAPIC flat addressing mode. */
+ KVM_APIC_MODE_XAPIC_FLAT,
+ /* All software enabled local APICs in x2APIC mode. */
+ KVM_APIC_MODE_X2APIC,
+ /*
+ * Optimized map disabled, e.g. not all local APICs in the same logical
+ * mode, same logical ID assigned to multiple APICs, etc.
+ */
+ KVM_APIC_MODE_MAP_DISABLED,
+};

struct kvm_apic_map {
struct rcu_head rcu;
- u8 mode;
+ enum kvm_apic_logical_mode logical_mode;
u32 max_apic_id;
union {
struct kvm_lapic *xapic_flat_map[8];
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 2aee712e42bb..2567998b692c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -168,7 +168,12 @@ static bool kvm_use_posted_timer_interrupt(struct kvm_vcpu *vcpu)

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) {
+ switch (map->logical_mode) {
+ case KVM_APIC_MODE_SW_DISABLED:
+ /* Arbitrarily use the flat map so that @cluster isn't NULL. */
+ *cluster = map->xapic_flat_map;
+ *mask = 0;
+ return true;
case KVM_APIC_MODE_X2APIC: {
u32 offset = (dest_id >> 16) * 16;
u32 max_apic_id = map->max_apic_id;
@@ -193,8 +198,10 @@ static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
*cluster = map->xapic_cluster_map[(dest_id >> 4) & 0xf];
*mask = dest_id & 0xf;
return true;
+ case KVM_APIC_MODE_MAP_DISABLED:
+ return false;
default:
- /* Not optimized. */
+ WARN_ON_ONCE(1);
return false;
}
}
@@ -256,10 +263,12 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
goto out;

new->max_apic_id = max_id;
+ new->logical_mode = KVM_APIC_MODE_SW_DISABLED;

kvm_for_each_vcpu(i, vcpu, kvm) {
struct kvm_lapic *apic = vcpu->arch.apic;
struct kvm_lapic **cluster;
+ enum kvm_apic_logical_mode logical_mode;
u16 mask;
u32 ldr;
u8 xapic_id;
@@ -282,7 +291,8 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id])
new->phys_map[xapic_id] = apic;

- if (!kvm_apic_sw_enabled(apic))
+ if (new->logical_mode == KVM_APIC_MODE_MAP_DISABLED ||
+ !kvm_apic_sw_enabled(apic))
continue;

ldr = kvm_lapic_get_reg(apic, APIC_LDR);
@@ -290,17 +300,31 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
continue;

if (apic_x2apic_mode(apic)) {
- new->mode |= KVM_APIC_MODE_X2APIC;
+ logical_mode = KVM_APIC_MODE_X2APIC;
} else {
ldr = GET_APIC_LOGICAL_ID(ldr);
if (kvm_lapic_get_reg(apic, APIC_DFR) == APIC_DFR_FLAT)
- new->mode |= KVM_APIC_MODE_XAPIC_FLAT;
+ logical_mode = KVM_APIC_MODE_XAPIC_FLAT;
else
- new->mode |= KVM_APIC_MODE_XAPIC_CLUSTER;
+ logical_mode = KVM_APIC_MODE_XAPIC_CLUSTER;
}

- if (!kvm_apic_map_get_logical_dest(new, ldr, &cluster, &mask))
+ /*
+ * To optimize logical mode delivery, all software-enabled APICs must
+ * be configured for the same mode.
+ */
+ if (new->logical_mode == KVM_APIC_MODE_SW_DISABLED) {
+ new->logical_mode = logical_mode;
+ } else if (new->logical_mode != logical_mode) {
+ new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
continue;
+ }
+
+ if (WARN_ON_ONCE(!kvm_apic_map_get_logical_dest(new, ldr,
+ &cluster, &mask))) {
+ new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
+ continue;
+ }

if (mask)
cluster[ffs(mask) - 1] = apic;
@@ -953,7 +977,7 @@ static bool kvm_apic_is_broadcast_dest(struct kvm *kvm, struct kvm_lapic **src,
{
if (kvm->arch.x2apic_broadcast_quirk_disabled) {
if ((irq->dest_id == APIC_BROADCAST &&
- map->mode != KVM_APIC_MODE_X2APIC))
+ map->logical_mode != KVM_APIC_MODE_X2APIC))
return true;
if (irq->dest_id == X2APIC_BROADCAST)
return true;
--
2.39.0.314.g84b9a713c41-goog