exec: qemu_ram_alloc_resizeable, qemu_ram_resize

Add API to allocate "resizeable" RAM.
This looks just like regular RAM generally, but
has a special property that only a portion of it
(used_length) is actually used, and migrated.

This used_length size can change across reboots.

Follow up patches will change used_length for such blocks at migration,
making it easier to extend devices using such RAM (notably ACPI,
but in the future thinkably other ROMs) without breaking migration
compatibility or wasting ROM (guest) memory.

Device is notified on resize, so it can adjust if necessary.

qemu_ram_alloc_resizeable allocates this memory, qemu_ram_resize resizes
it.

Note: nothing prevents making all RAM resizeable in this way.
However, reviewers felt that only enabling this selectively will
make some class of errors easier to detect.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 78 insertions, 4 deletions

diff --git a/exec.c b/exec.c
index b69216ab0e..58ac6d6630 100644
--- a/exec.c
+++ b/exec.c
@@ -75,6 +75,11 @@ static MemoryRegion io_mem_unassigned;
 /* RAM is mmap-ed with MAP_SHARED */
 #define RAM_SHARED     (1 << 1)
 
+/* Only a portion of RAM (used_length) is actually used, and migrated.
+ * This used_length size can change across reboots.
+ */
+#define RAM_RESIZEABLE (1 << 2)
+
 #endif
 
 struct CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
@@ -1186,7 +1191,7 @@ static ram_addr_t find_ram_offset(ram_addr_t size)
     QTAILQ_FOREACH(block, &ram_list.blocks, next) {
         ram_addr_t end, next = RAM_ADDR_MAX;
 
-        end = block->offset + block->length;
+        end = block->offset + block->max_length;
 
         QTAILQ_FOREACH(next_block, &ram_list.blocks, next) {
             if (next_block->offset >= end) {
@@ -1214,7 +1219,7 @@ ram_addr_t last_ram_offset(void)
     ram_addr_t last = 0;
 
     QTAILQ_FOREACH(block, &ram_list.blocks, next)
-        last = MAX(last, block->offset + block->length);
+        last = MAX(last, block->offset + block->max_length);
 
     return last;
 }
@@ -1296,6 +1301,49 @@ static int memory_try_enable_merging(void *addr, size_t len)
     return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE);
 }
 
+/* Only legal before guest might have detected the memory size: e.g. on
+ * incoming migration, or right after reset.
+ *
+ * As memory core doesn't know how is memory accessed, it is up to
+ * resize callback to update device state and/or add assertions to detect
+ * misuse, if necessary.
+ */
+int qemu_ram_resize(ram_addr_t base, ram_addr_t newsize, Error **errp)
+{
+    RAMBlock *block = find_ram_block(base);
+
+    assert(block);
+
+    if (block->used_length == newsize) {
+        return 0;
+    }
+
+    if (!(block->flags & RAM_RESIZEABLE)) {
+        error_setg_errno(errp, EINVAL,
+                         "Length mismatch: %s: 0x" RAM_ADDR_FMT
+                         " in != 0x" RAM_ADDR_FMT, block->idstr,
+                         newsize, block->used_length);
+        return -EINVAL;
+    }
+
+    if (block->max_length < newsize) {
+        error_setg_errno(errp, EINVAL,
+                         "Length too large: %s: 0x" RAM_ADDR_FMT
+                         " > 0x" RAM_ADDR_FMT, block->idstr,
+                         newsize, block->max_length);
+        return -EINVAL;
+    }
+
+    cpu_physical_memory_clear_dirty_range(block->offset, block->used_length);
+    block->used_length = newsize;
+    cpu_physical_memory_set_dirty_range(block->offset, block->used_length);
+    memory_region_set_size(block->mr, newsize);
+    if (block->resized) {
+        block->resized(block->idstr, newsize, block->host);
+    }
+    return 0;
+}
+
 static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp)
 {
     RAMBlock *block;
@@ -1413,7 +1461,12 @@ ram_addr_t qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
 }
 #endif
 
-ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
+static
+ram_addr_t qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
+                                   void (*resized)(const char*,
+                                                   uint64_t length,
+                                                   void *host),
+                                   void *host, bool resizeable,
                                    MemoryRegion *mr, Error **errp)
 {
     RAMBlock *new_block;
@@ -1421,15 +1474,21 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
     Error *local_err = NULL;
 
     size = TARGET_PAGE_ALIGN(size);
+    max_size = TARGET_PAGE_ALIGN(max_size);
     new_block = g_malloc0(sizeof(*new_block));
     new_block->mr = mr;
+    new_block->resized = resized;
     new_block->used_length = size;
     new_block->max_length = max_size;
+    assert(max_size >= size);
     new_block->fd = -1;
     new_block->host = host;
     if (host) {
         new_block->flags |= RAM_PREALLOC;
     }
+    if (resizeable) {
+        new_block->flags |= RAM_RESIZEABLE;
+    }
     addr = ram_block_add(new_block, &local_err);
     if (local_err) {
         g_free(new_block);
@@ -1439,9 +1498,24 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
     return addr;
 }
 
+ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
+                                   MemoryRegion *mr, Error **errp)
+{
+    return qemu_ram_alloc_internal(size, size, NULL, host, false, mr, errp);
+}
+
 ram_addr_t qemu_ram_alloc(ram_addr_t size, MemoryRegion *mr, Error **errp)
 {
-    return qemu_ram_alloc_from_ptr(size, NULL, mr, errp);
+    return qemu_ram_alloc_internal(size, size, NULL, NULL, false, mr, errp);
+}
+
+ram_addr_t qemu_ram_alloc_resizeable(ram_addr_t size, ram_addr_t maxsz,
+                                     void (*resized)(const char*,
+                                                     uint64_t length,
+                                                     void *host),
+                                     MemoryRegion *mr, Error **errp)
+{
+    return qemu_ram_alloc_internal(size, maxsz, resized, NULL, true, mr, errp);
 }
 
 void qemu_ram_free_from_ptr(ram_addr_t addr)