[Qemu-devel] [PATCH v2] kvm: Detect number of available memory slots from the host kernel

[Alex Williamson <alex.williamson@redhat.com>]

The kernel already exposes an interface for this, x86 returns a proper
value and for the rest we can default to the defacto standard of 32.
The primary motivation for this is to support more PCI assigned
devices, both through pci-assign and vfio-pci.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
v2: Test (!num_slots) instead of (num_slots <= 0)

 kvm-all.c |   27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index 8e9a8d8..74cf0d6 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -71,7 +71,8 @@ typedef struct kvm_dirty_log KVMDirtyLog;
 
 struct KVMState
 {
-    KVMSlot slots[32];
+    KVMSlot *slots;
+    int num_slots;
     int fd;
     int vmfd;
     int coalesced_mmio;
@@ -120,7 +121,7 @@ static KVMSlot *kvm_alloc_slot(KVMState *s)
 {
     int i;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->num_slots; i++) {
         if (s->slots[i].memory_size == 0) {
             return &s->slots[i];
         }
@@ -136,7 +137,7 @@ static KVMSlot *kvm_lookup_matching_slot(KVMState *s,
 {
     int i;
 
-    for (i = 0; i < ARRAY_SIZE(s->slots); i++) {
+    for (i = 0; i < s->num_slots; i++) {
         KVMSlot *mem = &s->slots[i];
 
         if (start_addr == mem->start_addr &&
@@ -158,7 +159,7 @@ 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->num_slots; i++) {
         KVMSlot *mem = &s->slots[i];
 
         if (mem->memory_size == 0 ||
@@ -180,7 +181,7 @@ 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->num_slots; i++) {
         KVMSlot *mem = &s->slots[i];
 
         if (ram >= mem->ram && ram < mem->ram + mem->memory_size) {
@@ -340,7 +341,7 @@ 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->num_slots; i++) {
         mem = &s->slots[i];
 
         if (!mem->memory_size) {
@@ -1268,9 +1269,6 @@ 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) {
@@ -1324,6 +1322,16 @@ int kvm_init(void)
         goto err;
     }
 
+    s->num_slots = kvm_check_extension(s, KVM_CAP_NR_MEMSLOTS);
+    if (!s->num_slots) {
+        s->num_slots = 32;
+    }
+    s->slots = g_malloc0(s->num_slots * sizeof(*s->slots));
+
+    for (i = 0; i < s->num_slots; i++) {
+        s->slots[i].slot = i;
+    }
+
     s->coalesced_mmio = kvm_check_extension(s, KVM_CAP_COALESCED_MMIO);
 
     s->broken_set_mem_region = 1;
@@ -1393,6 +1401,7 @@ err:
     if (s->fd != -1) {
         close(s->fd);
     }
+    g_free(s->slots);
     g_free(s);
 
     return ret;