kvm: Query KVM for available memory slots

KVM reports the number of available memory slots (KVM_CAP_NR_MEMSLOTS)
using the extension interface.  Both x86 and s390 implement this, ARM
and powerpc do not yet enable it.  Convert the static slots array to
be dynamically allocated, supporting more slots when available.
Default to 32 when KVM_CAP_NR_MEMSLOTS is not implemented.  The
motivation for this change is to support more assigned devices, where
memory mapped PCI MMIO BARs typically take one slot each.
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Reviewed-by: NThomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

kvm-all.c

@@ -72,7 +72,8 @@ typedef struct kvm_dirty_log KVMDirtyLog;
 
 struct KVMState
 {
-    KVMSlot slots[32];
+    KVMSlot *slots;
+    int nr_slots;
     int fd;
     int vmfd;
     int coalesced_mmio;
@@ -125,7 +126,7 @@ static KVMSlot *kvm_alloc_slot(KVMState *s)
 {
     int i;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->nr_slots; i++) {
         if (s->slots[i].memory_size == 0) {
             return &s->slots[i];
         }
@@ -141,7 +142,7 @@ static KVMSlot *kvm_lookup_matching_slot(KVMState *s,
 {
     int i;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->nr_slots; i++) {
         KVMSlot *mem = &s->slots[i];
 
         if (start_addr == mem->start_addr &&
@@ -163,7 +164,7 @@ static KVMSlot *kvm_lookup_overlapping_slot(KVMState *s,
     KVMSlot *found = NULL;
     int i;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->nr_slots; i++) {
         KVMSlot *mem = &s->slots[i];
 
         if (mem->memory_size == 0 ||
@@ -185,7 +186,7 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
 {
     int i;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->nr_slots; i++) {
         KVMSlot *mem = &s->slots[i];
 
         if (ram >= mem->ram && ram < mem->ram + mem->memory_size) {
@@ -357,7 +358,7 @@ static int kvm_set_migration_log(int enable)
 
     s->migration_log = enable;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->nr_slots; i++) {
         mem = &s->slots[i];
 
         if (!mem->memory_size) {
@@ -1383,9 +1384,6 @@ int kvm_init(void)
 #ifdef KVM_CAP_SET_GUEST_DEBUG
     QTAILQ_INIT(&s->kvm_sw_breakpoints);
 #endif
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
-        s->slots[i].slot = i;
-    }
     s->vmfd = -1;
     s->fd = qemu_open("/dev/kvm", O_RDWR);
     if (s->fd == -1) {
@@ -1409,6 +1407,19 @@ int kvm_init(void)
         goto err;
     }
 
+    s->nr_slots = kvm_check_extension(s, KVM_CAP_NR_MEMSLOTS);
+
+    /* If unspecified, use the default value */
+    if (!s->nr_slots) {
+        s->nr_slots = 32;
+    }
+
+    s->slots = g_malloc0(s->nr_slots * sizeof(KVMSlot));
+
+    for (i = 0; i < s->nr_slots; i++) {
+        s->slots[i].slot = i;
+    }
+
     /* check the vcpu limits */
     soft_vcpus_limit = kvm_recommended_vcpus(s);
     hard_vcpus_limit = kvm_max_vcpus(s);
@@ -1527,6 +1538,7 @@ err:
     if (s->fd != -1) {
         close(s->fd);
     }
+    g_free(s->slots);
     g_free(s);
 
     return ret;