KVM: Use a big lock to replace per-kml slots_lock

Per-kml slots_lock will bring some trouble if we want to take all slots_lock of
all the KMLs, especially when we're in a context that we could have taken some
of the KML slots_lock, then we even need to figure out what we've taken and
what we need to take.

Make this simple by merging all KML slots_lock into a single slots lock.

Per-kml slots_lock isn't anything that helpful anyway - so far only x86 has two
address spaces (so, two slots_locks).  All the rest archs will be having one
address space always, which means there's actually one slots_lock so it will be
the same as before.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210506160549.130416-3-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -172,8 +172,10 @@ typedef struct KVMResampleFd KVMResampleFd;
 static QLIST_HEAD(, KVMResampleFd) kvm_resample_fd_list =
     QLIST_HEAD_INITIALIZER(kvm_resample_fd_list);
 
-#define kvm_slots_lock(kml)      qemu_mutex_lock(&(kml)->slots_lock)
+static QemuMutex kml_slots_lock;
-#define kvm_slots_unlock(kml)    qemu_mutex_unlock(&(kml)->slots_lock)
+
+#define kvm_slots_lock()    qemu_mutex_lock(&kml_slots_lock)
+#define kvm_slots_unlock()  qemu_mutex_unlock(&kml_slots_lock)
 
 static inline void kvm_resample_fd_remove(int gsi)
 {
@@ -239,9 +241,9 @@ bool kvm_has_free_slot(MachineState *ms)
     bool result;
     KVMMemoryListener *kml = &s->memory_listener;
 
-    kvm_slots_lock(kml);
+    kvm_slots_lock();
     result = !!kvm_get_free_slot(kml);
-    kvm_slots_unlock(kml);
+    kvm_slots_unlock();
 
     return result;
 }
@@ -307,7 +309,7 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
     KVMMemoryListener *kml = &s->memory_listener;
     int i, ret = 0;
 
-    kvm_slots_lock(kml);
+    kvm_slots_lock();
     for (i = 0; i < s->nr_slots; i++) {
         KVMSlot *mem = &kml->slots[i];
 
@@ -317,7 +319,7 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
             break;
         }
     }
-    kvm_slots_unlock(kml);
+    kvm_slots_unlock();
 
     return ret;
 }
@@ -513,7 +515,7 @@ static int kvm_section_update_flags(KVMMemoryListener *kml,
         return 0;
     }
 
-    kvm_slots_lock(kml);
+    kvm_slots_lock();
 
     while (size && !ret) {
         slot_size = MIN(kvm_max_slot_size, size);
@@ -529,7 +531,7 @@ static int kvm_section_update_flags(KVMMemoryListener *kml,
     }
 
 out:
-    kvm_slots_unlock(kml);
+    kvm_slots_unlock();
     return ret;
 }
 
@@ -810,7 +812,7 @@ static int kvm_physical_log_clear(KVMMemoryListener *kml,
         return ret;
     }
 
-    kvm_slots_lock(kml);
+    kvm_slots_lock();
 
     for (i = 0; i < s->nr_slots; i++) {
         mem = &kml->slots[i];
@@ -836,7 +838,7 @@ static int kvm_physical_log_clear(KVMMemoryListener *kml,
         }
     }
 
-    kvm_slots_unlock(kml);
+    kvm_slots_unlock();
 
     return ret;
 }
@@ -1141,7 +1143,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
     ram = memory_region_get_ram_ptr(mr) + section->offset_within_region +
           (start_addr - section->offset_within_address_space);
 
-    kvm_slots_lock(kml);
+    kvm_slots_lock();
 
     if (!add) {
         do {
@@ -1199,7 +1201,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
     } while (size);
 
 out:
-    kvm_slots_unlock(kml);
+    kvm_slots_unlock();
 }
 
 static void kvm_region_add(MemoryListener *listener,
@@ -1226,9 +1228,9 @@ static void kvm_log_sync(MemoryListener *listener,
     KVMMemoryListener *kml = container_of(listener, KVMMemoryListener, listener);
     int r;
 
-    kvm_slots_lock(kml);
+    kvm_slots_lock();
     r = kvm_physical_sync_dirty_bitmap(kml, section);
-    kvm_slots_unlock(kml);
+    kvm_slots_unlock();
     if (r < 0) {
         abort();
     }
@@ -1328,7 +1330,6 @@ void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
 {
     int i;
 
-    qemu_mutex_init(&kml->slots_lock);
     kml->slots = g_malloc0(s->nr_slots * sizeof(KVMSlot));
     kml->as_id = as_id;
 
@@ -2001,6 +2002,8 @@ static int kvm_init(MachineState *ms)
     int type = 0;
     uint64_t dirty_log_manual_caps;
 
+    qemu_mutex_init(&kml_slots_lock);
+
     s = KVM_STATE(ms->accelerator);
 
     /*

include/sysemu/kvm_int.h

@@ -27,8 +27,6 @@ typedef struct KVMSlot
 
 typedef struct KVMMemoryListener {
     MemoryListener listener;
-    /* Protects the slots and all inside them */
-    QemuMutex slots_lock;
     KVMSlot *slots;
     int as_id;
 } KVMMemoryListener;