kvm: Return number of free memslots

Let's return the number of free slots instead of only checking if there
is a free slot. While at it, check all address spaces, which will also
consider SMM under x86 correctly.

This is a preparation for memory devices that consume multiple memslots.

Message-ID: <20230926185738.277351-5-david@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

accel/kvm/kvm-all.c

@@ -181,6 +181,24 @@ int kvm_get_max_memslots(void)
     return s->nr_slots;
 }
 
+unsigned int kvm_get_free_memslots(void)
+{
+    unsigned int used_slots = 0;
+    KVMState *s = kvm_state;
+    int i;
+
+    kvm_slots_lock();
+    for (i = 0; i < s->nr_as; i++) {
+        if (!s->as[i].ml) {
+            continue;
+        }
+        used_slots = MAX(used_slots, s->as[i].ml->nr_used_slots);
+    }
+    kvm_slots_unlock();
+
+    return s->nr_slots - used_slots;
+}
+
 /* Called with KVMMemoryListener.slots_lock held */
 static KVMSlot *kvm_get_free_slot(KVMMemoryListener *kml)
 {
@@ -196,19 +214,6 @@ static KVMSlot *kvm_get_free_slot(KVMMemoryListener *kml)
     return NULL;
 }
 
-bool kvm_has_free_slot(MachineState *ms)
-{
-    KVMState *s = KVM_STATE(ms->accelerator);
-    bool result;
-    KVMMemoryListener *kml = &s->memory_listener;
-
-    kvm_slots_lock();
-    result = !!kvm_get_free_slot(kml);
-    kvm_slots_unlock();
-
-    return result;
-}
-
 /* Called with KVMMemoryListener.slots_lock held */
 static KVMSlot *kvm_alloc_slot(KVMMemoryListener *kml)
 {
@@ -1387,6 +1392,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
             }
             start_addr += slot_size;
             size -= slot_size;
+            kml->nr_used_slots--;
         } while (size);
         return;
     }
@@ -1412,6 +1418,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
         ram_start_offset += slot_size;
         ram += slot_size;
         size -= slot_size;
+        kml->nr_used_slots++;
     } while (size);
 }
 

accel/stubs/kvm-stub.c

@@ -109,9 +109,9 @@ int kvm_irqchip_remove_irqfd_notifier_gsi(KVMState *s, EventNotifier *n,
     return -ENOSYS;
 }
 
-bool kvm_has_free_slot(MachineState *ms)
+unsigned int kvm_get_free_memslots(void)
 {
-    return false;
+    return 0;
 }
 
 void kvm_init_cpu_signals(CPUState *cpu)

hw/mem/memory-device.c

@@ -59,7 +59,7 @@ static void memory_device_check_addable(MachineState *ms, MemoryRegion *mr,
     const uint64_t size = memory_region_size(mr);
 
     /* we will need a new memory slot for kvm and vhost */
-    if (kvm_enabled() && !kvm_has_free_slot(ms)) {
+    if (kvm_enabled() && !kvm_get_free_memslots()) {
         error_setg(errp, "hypervisor has no free memory slots left");
         return;
     }

include/sysemu/kvm.h

@@ -215,7 +215,7 @@ typedef struct KVMRouteChange {
 
 /* external API */
 
-bool kvm_has_free_slot(MachineState *ms);
+unsigned int kvm_get_free_memslots(void);
 bool kvm_has_sync_mmu(void);
 int kvm_has_vcpu_events(void);
 int kvm_has_robust_singlestep(void);

include/sysemu/kvm_int.h

@@ -40,6 +40,7 @@ typedef struct KVMMemoryUpdate {
 typedef struct KVMMemoryListener {
     MemoryListener listener;
     KVMSlot *slots;
+    unsigned int nr_used_slots;
     int as_id;
     QSIMPLEQ_HEAD(, KVMMemoryUpdate) transaction_add;
     QSIMPLEQ_HEAD(, KVMMemoryUpdate) transaction_del;