[PATCH PROTOTYPE 4/6] memory: Extend ram_block_discard_(require|disable) by two discard types

[David Hildenbrand]

We want to separate the two cases whereby
- balloning drivers do random discards on random guest memory (e.g.,
  virtio-balloon) - uncoordinated discards
- paravirtualized memory devices do discards in well-known granularity,
  and always know which block is currently accessible or inaccessible by
  a guest. - coordinated discards

This will be required to get virtio_mem + vfio running - vfio still
wants to block random memory ballooning.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.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>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 exec.c                | 109 ++++++++++++++++++++++++++++++++++--------
 include/exec/memory.h |  36 ++++++++++++--
 2 files changed, 121 insertions(+), 24 deletions(-)

diff --git a/exec.c b/exec.c
index e34b602bdf..83098e9230 100644
--- a/exec.c
+++ b/exec.c
@@ -4098,52 +4098,121 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, 
MemoryRegion *root)
  * If positive, discarding RAM is disabled. If negative, discarding RAM is
  * required to work and cannot be disabled.
  */
-static int ram_block_discard_disabled;
+static int uncoordinated_discard_disabled;
+static int coordinated_discard_disabled;
 
-int ram_block_discard_disable(bool state)
+static int __ram_block_discard_disable(int *counter)
 {
     int old;
 
-    if (!state) {
-        atomic_dec(&ram_block_discard_disabled);
-        return 0;
-    }
-
     do {
-        old = atomic_read(&ram_block_discard_disabled);
+        old = atomic_read(counter);
         if (old < 0) {
             return -EBUSY;
         }
-    } while (atomic_cmpxchg(&ram_block_discard_disabled, old, old + 1) != old);
+    } while (atomic_cmpxchg(counter, old, old + 1) != old);
+
     return 0;
 }
 
-int ram_block_discard_require(bool state)
+int ram_block_discard_type_disable(RamBlockDiscardType type, bool state)
 {
-    int old;
+    int ret;
 
-    if (!state) {
-        atomic_inc(&ram_block_discard_disabled);
-        return 0;
+    if (type & RAM_BLOCK_DISCARD_T_UNCOORDINATED) {
+        if (!state) {
+            atomic_dec(&uncoordinated_discard_disabled);
+        } else {
+            ret = __ram_block_discard_disable(&uncoordinated_discard_disabled);
+            if (ret) {
+                return ret;
+            }
+        }
     }
+    if (type & RAM_BLOCK_DISCARD_T_COORDINATED) {
+        if (!state) {
+            atomic_dec(&coordinated_discard_disabled);
+        } else {
+            ret = __ram_block_discard_disable(&coordinated_discard_disabled);
+            if (ret) {
+                /* Rollback the previous change. */
+                if (type & RAM_BLOCK_DISCARD_T_UNCOORDINATED) {
+                    atomic_dec(&uncoordinated_discard_disabled);
+                }
+                return ret;
+            }
+        }
+    }
+    return 0;
+}
+
+static int __ram_block_discard_require(int *counter)
+{
+    int old;
 
     do {
-        old = atomic_read(&ram_block_discard_disabled);
+        old = atomic_read(counter);
         if (old > 0) {
             return -EBUSY;
         }
-    } while (atomic_cmpxchg(&ram_block_discard_disabled, old, old - 1) != old);
+    } while (atomic_cmpxchg(counter, old, old - 1) != old);
+
+    return 0;
+}
+
+int ram_block_discard_type_require(RamBlockDiscardType type, bool state)
+{
+    int ret;
+
+    if (type & RAM_BLOCK_DISCARD_T_UNCOORDINATED) {
+        if (!state) {
+            atomic_inc(&uncoordinated_discard_disabled);
+        } else {
+            ret = __ram_block_discard_require(&uncoordinated_discard_disabled);
+            if (ret) {
+                return ret;
+            }
+        }
+    }
+    if (type & RAM_BLOCK_DISCARD_T_COORDINATED) {
+        if (!state) {
+            atomic_inc(&coordinated_discard_disabled);
+        } else {
+            ret = __ram_block_discard_require(&coordinated_discard_disabled);
+            if (ret) {
+                /* Rollback the previous change. */
+                if (type & RAM_BLOCK_DISCARD_T_UNCOORDINATED) {
+                    atomic_inc(&uncoordinated_discard_disabled);
+                }
+                return ret;
+            }
+        }
+    }
     return 0;
 }
 
-bool ram_block_discard_is_disabled(void)
+bool ram_block_discard_type_is_disabled(RamBlockDiscardType type)
 {
-    return atomic_read(&ram_block_discard_disabled) > 0;
+    if (type & RAM_BLOCK_DISCARD_T_UNCOORDINATED &&
+        atomic_read(&uncoordinated_discard_disabled) > 0) {
+        return true;
+    } else if (type & RAM_BLOCK_DISCARD_T_COORDINATED &&
+               atomic_read(&coordinated_discard_disabled) > 0) {
+        return true;
+    }
+    return false;
 }
 
-bool ram_block_discard_is_required(void)
+bool ram_block_discard_type_is_required(RamBlockDiscardType type)
 {
-    return atomic_read(&ram_block_discard_disabled) < 0;
+    if (type & RAM_BLOCK_DISCARD_T_UNCOORDINATED &&
+        atomic_read(&uncoordinated_discard_disabled) < 0) {
+        return true;
+    } else if (type & RAM_BLOCK_DISCARD_T_COORDINATED &&
+               atomic_read(&coordinated_discard_disabled) < 0) {
+        return true;
+    }
+    return false;
 }
 
 #endif
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 2931ead730..3169ebc3d9 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2588,6 +2588,18 @@ static inline MemOp devend_memop(enum device_endian end)
 }
 #endif
 
+typedef enum RamBlockDiscardType {
+    /* Uncorrdinated discards (e.g., virtio-balloon */
+    RAM_BLOCK_DISCARD_T_UNCOORDINATED = 1,
+    /*
+     * Coordinated discards on selected memory regions (e.g., virtio-mem via
+     * SparseRamNotifier).
+     */
+    RAM_BLOCK_DISCARD_T_COORDINATED =   2,
+    /* Any type of discards */
+    RAM_BLOCK_DISCARD_T_ANY =           3,
+} RamBlockDiscardType;
+
 /*
  * Inhibit technologies that require discarding of pages in RAM blocks, e.g.,
  * to manage the actual amount of memory consumed by the VM (then, the memory
@@ -2609,7 +2621,11 @@ static inline MemOp devend_memop(enum device_endian end)
  * Returns 0 if successful. Returns -EBUSY if a technology that relies on
  * discards to work reliably is active.
  */
-int ram_block_discard_disable(bool state);
+int ram_block_discard_type_disable(RamBlockDiscardType type, bool state);
+static inline int ram_block_discard_disable(bool state)
+{
+    return ram_block_discard_type_disable(RAM_BLOCK_DISCARD_T_ANY, state);
+}
 
 /*
  * Inhibit technologies that disable discarding of pages in RAM blocks.
@@ -2617,17 +2633,29 @@ int ram_block_discard_disable(bool state);
  * Returns 0 if successful. Returns -EBUSY if discards are already set to
  * broken.
  */
-int ram_block_discard_require(bool state);
+int ram_block_discard_type_require(RamBlockDiscardType type, bool state);
+static inline int ram_block_discard_require(bool state)
+{
+    return ram_block_discard_type_require(RAM_BLOCK_DISCARD_T_ANY, state);
+}
 
 /*
  * Test if discarding of memory in ram blocks is disabled.
  */
-bool ram_block_discard_is_disabled(void);
+bool ram_block_discard_type_is_disabled(RamBlockDiscardType type);
+static inline bool ram_block_discard_is_disabled(void)
+{
+    return ram_block_discard_type_is_disabled(RAM_BLOCK_DISCARD_T_ANY);
+}
 
 /*
  * Test if discarding of memory in ram blocks is required to work reliably.
  */
-bool ram_block_discard_is_required(void);
+bool ram_block_discard_type_is_required(RamBlockDiscardType type);
+static inline bool ram_block_discard_is_required(void)
+{
+    return ram_block_discard_type_is_required(RAM_BLOCK_DISCARD_T_ANY);
+}
 
 #endif
 
-- 
2.26.2