softmmu/physmem: Extend ram_block_discard_(require|disable) by two discard types

We want to separate the two cases whereby we discard ram
- uncoordinated: e.g., virito-balloon
- coordinated: e.g., virtio-mem coordinated via the RamDiscardManager

Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-12-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

include/exec/memory.h

@@ -2893,6 +2893,12 @@ static inline MemOp devend_memop(enum device_endian end)
  */
 int ram_block_discard_disable(bool state);
 
+/*
+ * See ram_block_discard_disable(): only disable uncoordinated discards,
+ * keeping coordinated discards (via the RamDiscardManager) enabled.
+ */
+int ram_block_uncoordinated_discard_disable(bool state);
+
 /*
  * Inhibit technologies that disable discarding of pages in RAM blocks.
  *
@@ -2902,12 +2908,20 @@ int ram_block_discard_disable(bool state);
 int ram_block_discard_require(bool state);
 
 /*
- * Test if discarding of memory in ram blocks is disabled.
+ * See ram_block_discard_require(): only inhibit technologies that disable
+ * uncoordinated discarding of pages in RAM blocks, allowing co-existance with
+ * technologies that only inhibit uncoordinated discards (via the
+ * RamDiscardManager).
+ */
+int ram_block_coordinated_discard_require(bool state);
+
+/*
+ * Test if any discarding of memory in ram blocks is disabled.
  */
 bool ram_block_discard_is_disabled(void);
 
 /*
- * Test if discarding of memory in ram blocks is required to work reliably.
+ * Test if any discarding of memory in ram blocks is required to work reliably.
  */
 bool ram_block_discard_is_required(void);
 

softmmu/physmem.c

@@ -3684,8 +3684,14 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root)
     }
 }
 
+/* Require any discards to work. */
 static unsigned int ram_block_discard_required_cnt;
+/* Require only coordinated discards to work. */
+static unsigned int ram_block_coordinated_discard_required_cnt;
+/* Disable any discards. */
 static unsigned int ram_block_discard_disabled_cnt;
+/* Disable only uncoordinated discards. */
+static unsigned int ram_block_uncoordinated_discard_disabled_cnt;
 static QemuMutex ram_block_discard_disable_mutex;
 
 static void ram_block_discard_disable_mutex_lock(void)
@@ -3711,10 +3717,27 @@ int ram_block_discard_disable(bool state)
     ram_block_discard_disable_mutex_lock();
     if (!state) {
         ram_block_discard_disabled_cnt--;
-    } else if (!ram_block_discard_required_cnt) {
+    } else if (ram_block_discard_required_cnt ||
-        ram_block_discard_disabled_cnt++;
+               ram_block_coordinated_discard_required_cnt) {
-    } else {
         ret = -EBUSY;
+    } else {
+        ram_block_discard_disabled_cnt++;
+    }
+    ram_block_discard_disable_mutex_unlock();
+    return ret;
+}
+
+int ram_block_uncoordinated_discard_disable(bool state)
+{
+    int ret = 0;
+
+    ram_block_discard_disable_mutex_lock();
+    if (!state) {
+        ram_block_uncoordinated_discard_disabled_cnt--;
+    } else if (ram_block_discard_required_cnt) {
+        ret = -EBUSY;
+    } else {
+        ram_block_uncoordinated_discard_disabled_cnt++;
     }
     ram_block_discard_disable_mutex_unlock();
     return ret;
@@ -3727,10 +3750,27 @@ int ram_block_discard_require(bool state)
     ram_block_discard_disable_mutex_lock();
     if (!state) {
         ram_block_discard_required_cnt--;
-    } else if (!ram_block_discard_disabled_cnt) {
+    } else if (ram_block_discard_disabled_cnt ||
-        ram_block_discard_required_cnt++;
+               ram_block_uncoordinated_discard_disabled_cnt) {
-    } else {
         ret = -EBUSY;
+    } else {
+        ram_block_discard_required_cnt++;
+    }
+    ram_block_discard_disable_mutex_unlock();
+    return ret;
+}
+
+int ram_block_coordinated_discard_require(bool state)
+{
+    int ret = 0;
+
+    ram_block_discard_disable_mutex_lock();
+    if (!state) {
+        ram_block_coordinated_discard_required_cnt--;
+    } else if (ram_block_discard_disabled_cnt) {
+        ret = -EBUSY;
+    } else {
+        ram_block_coordinated_discard_required_cnt++;
     }
     ram_block_discard_disable_mutex_unlock();
     return ret;
@@ -3738,10 +3778,12 @@ int ram_block_discard_require(bool state)
 
 bool ram_block_discard_is_disabled(void)
 {
-    return qatomic_read(&ram_block_discard_disabled_cnt);
+    return qatomic_read(&ram_block_discard_disabled_cnt) ||
+           qatomic_read(&ram_block_uncoordinated_discard_disabled_cnt);
 }
 
 bool ram_block_discard_is_required(void)
 {
-    return qatomic_read(&ram_block_discard_required_cnt);
+    return qatomic_read(&ram_block_discard_required_cnt) ||
+           qatomic_read(&ram_block_coordinated_discard_required_cnt);
 }