[PATCH v5 33/33] KVM: x86: Add helpers to recalc physical vs. logical optimized APIC maps

Sean Christopherson
2023-01-06T01:18:24Z

Move the guts of kvm_recalculate_apic_map()'s main loop to two separate
helpers to handle recalculating the physical and logical pieces of the
optimized map. Having 100+ lines of code in the for-loop makes it hard
to understand what is being calculated where.

No functional change intended.

Suggested-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/lapic.c | 250 +++++++++++++++++++++++--------------------
1 file changed, 133 insertions(+), 117 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 856e81a2dc64..669ea125b7e2 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -218,6 +218,134 @@ static void kvm_apic_map_free(struct rcu_head *rcu)
kvfree(map);
}

+static int kvm_recalculate_phys_map(struct kvm_apic_map *new,
+ struct kvm_vcpu *vcpu,
+ bool *xapic_id_mismatch)
+{
+ struct kvm_lapic *apic = vcpu->arch.apic;
+ u32 x2apic_id = kvm_x2apic_id(apic);
+ u32 xapic_id = kvm_xapic_id(apic);
+ u32 physical_id;
+
+ /*
+ * Deliberately truncate the vCPU ID when detecting a mismatched APIC
+ * ID to avoid false positives if the vCPU ID, i.e. x2APIC ID, is a
+ * 32-bit value. Any unwanted aliasing due to truncation results will
+ * be detected below.
+ */
+ if (!apic_x2apic_mode(apic) && xapic_id != (u8)vcpu->vcpu_id)
+ *xapic_id_mismatch = true;
+
+ /*
+ * Apply KVM's hotplug hack if userspace has enable 32-bit APIC IDs.
+ * Allow sending events to vCPUs by their x2APIC ID even if the target
+ * vCPU is in legacy xAPIC mode, and silently ignore aliased xAPIC IDs
+ * (the x2APIC ID is truncated to 8 bits, causing IDs > 0xff to wrap
+ * and collide).
+ *
+ * Honor the architectural (and KVM's non-optimized) behavior if
+ * userspace has not enabled 32-bit x2APIC IDs. Each APIC is supposed
+ * to process messages independently. If multiple vCPUs have the same
+ * effective APIC ID, e.g. due to the x2APIC wrap or because the guest
+ * manually modified its xAPIC IDs, events targeting that ID are
+ * supposed to be recognized by all vCPUs with said ID.
+ */
+ if (vcpu->kvm->arch.x2apic_format) {
+ /* See also 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;
+
+ if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id])
+ new->phys_map[xapic_id] = apic;
+ } else {
+ /*
+ * Disable the optimized map if the physical APIC ID is already
+ * mapped, i.e. is aliased to multiple vCPUs. The optimized
+ * map requires a strict 1:1 mapping between IDs and vCPUs.
+ */
+ if (apic_x2apic_mode(apic))
+ physical_id = x2apic_id;
+ else
+ physical_id = xapic_id;
+
+ if (new->phys_map[physical_id])
+ return -EINVAL;
+
+ new->phys_map[physical_id] = apic;
+ }
+
+ return 0;
+}
+
+static void kvm_recalculate_logical_map(struct kvm_apic_map *new,
+ struct kvm_vcpu *vcpu)
+{
+ struct kvm_lapic *apic = vcpu->arch.apic;
+ enum kvm_apic_logical_mode logical_mode;
+ struct kvm_lapic **cluster;
+ u16 mask;
+ u32 ldr;
+
+ if (new->logical_mode == KVM_APIC_MODE_MAP_DISABLED)
+ return;
+
+ if (!kvm_apic_sw_enabled(apic))
+ return;
+
+ ldr = kvm_lapic_get_reg(apic, APIC_LDR);
+ if (!ldr)
+ return;
+
+ if (apic_x2apic_mode(apic)) {
+ logical_mode = KVM_APIC_MODE_X2APIC;
+ } else {
+ ldr = GET_APIC_LOGICAL_ID(ldr);
+ if (kvm_lapic_get_reg(apic, APIC_DFR) == APIC_DFR_FLAT)
+ logical_mode = KVM_APIC_MODE_XAPIC_FLAT;
+ else
+ logical_mode = KVM_APIC_MODE_XAPIC_CLUSTER;
+ }
+
+ /*
+ * 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;
+ return;
+ }
+
+ /*
+ * In x2APIC mode, the LDR is read-only and derived directly from the
+ * x2APIC ID, thus is guaranteed to be addressable. KVM reuses
+ * kvm_apic_map.phys_map to optimize logical mode x2APIC interrupts by
+ * reversing the LDR calculation to get cluster of APICs, i.e. no
+ * additional work is required.
+ */
+ if (apic_x2apic_mode(apic)) {
+ WARN_ON_ONCE(ldr != kvm_apic_calc_x2apic_ldr(kvm_x2apic_id(apic)));
+ return;
+ }
+
+ if (WARN_ON_ONCE(!kvm_apic_map_get_logical_dest(new, ldr,
+ &cluster, &mask))) {
+ new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
+ return;
+ }
+
+ if (!mask)
+ return;
+
+ ldr = ffs(mask) - 1;
+ if (!is_power_of_2(mask) || cluster[ldr])
+ new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
+ else
+ cluster[ldr] = apic;
+}
+
/*
* CLEAN -> DIRTY and UPDATE_IN_PROGRESS -> DIRTY changes happen without a lock.
*
@@ -272,128 +400,16 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
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;
- u32 x2apic_id, physical_id;
- u16 mask;
- u32 ldr;
- u8 xapic_id;
-
if (!kvm_apic_present(vcpu))
continue;

- xapic_id = kvm_xapic_id(apic);
- x2apic_id = kvm_x2apic_id(apic);
-
- /*
- * Deliberately truncate the vCPU ID when detecting a mismatched
- * APIC ID to avoid false positives if the vCPU ID, i.e. x2APIC
- * ID, is a 32-bit value. Any unwanted aliasing due to
- * truncation results will be detected below.
- */
- if (!apic_x2apic_mode(apic) && xapic_id != (u8)vcpu->vcpu_id)
- xapic_id_mismatch = true;
-
- /*
- * Apply KVM's hotplug hack if userspace has enable 32-bit APIC
- * IDs. Allow sending events to vCPUs by their x2APIC ID even
- * if the target vCPU is in legacy xAPIC mode, and silently
- * ignore aliased xAPIC IDs (the x2APIC ID is truncated to 8
- * bits, causing IDs > 0xff to wrap and collide).
- *
- * Honor the architectural (and KVM's non-optimized) behavior
- * if userspace has not enabled 32-bit x2APIC IDs. Each APIC
- * is supposed to process messages independently. If multiple
- * vCPUs have the same effective APIC ID, e.g. due to the
- * x2APIC wrap or because the guest manually modified its xAPIC
- * IDs, events targeting that ID are supposed to be recognized
- * by all vCPUs with said ID.
- */
- if (kvm->arch.x2apic_format) {
- /* See also 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;
-
- if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id])
- new->phys_map[xapic_id] = apic;
- } else {
- /*
- * Disable the optimized map if the physical APIC ID is
- * already mapped, i.e. is aliased to multiple vCPUs.
- * The optimized map requires a strict 1:1 mapping
- * between IDs and vCPUs.
- */
- if (apic_x2apic_mode(apic))
- physical_id = x2apic_id;
- else
- physical_id = xapic_id;
-
- if (new->phys_map[physical_id]) {
- kvfree(new);
- new = NULL;
- goto out;
- }
- new->phys_map[physical_id] = apic;
- }
-
- if (new->logical_mode == KVM_APIC_MODE_MAP_DISABLED ||
- !kvm_apic_sw_enabled(apic))
- continue;
-
- ldr = kvm_lapic_get_reg(apic, APIC_LDR);
- if (!ldr)
- continue;
-
- if (apic_x2apic_mode(apic)) {
- logical_mode = KVM_APIC_MODE_X2APIC;
- } else {
- ldr = GET_APIC_LOGICAL_ID(ldr);
- if (kvm_lapic_get_reg(apic, APIC_DFR) == APIC_DFR_FLAT)
- logical_mode = KVM_APIC_MODE_XAPIC_FLAT;
- else
- logical_mode = KVM_APIC_MODE_XAPIC_CLUSTER;
+ if (kvm_recalculate_phys_map(new, vcpu, &xapic_id_mismatch)) {
+ kvfree(new);
+ new = NULL;
+ goto out;
}

- /*
- * 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;
- }
-
- /*
- * In x2APIC mode, the LDR is read-only and derived directly
- * from the x2APIC ID, thus is guaranteed to be addressable.
- * KVM reuses kvm_apic_map.phys_map to optimize logical mode
- * x2APIC interrupts by reversing the LDR calculation to get
- * cluster of APICs, i.e. no additional work is required.
- */
- if (apic_x2apic_mode(apic)) {
- WARN_ON_ONCE(ldr != kvm_apic_calc_x2apic_ldr(x2apic_id));
- 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)
- continue;
-
- ldr = ffs(mask) - 1;
- if (!is_power_of_2(mask) || cluster[ldr]) {
- new->logical_mode = KVM_APIC_MODE_MAP_DISABLED;
- continue;
- }
- cluster[ldr] = apic;
+ kvm_recalculate_logical_map(new, vcpu);
}
out:
/*
--
2.39.0.314.g84b9a713c41-goog