[Qemu-devel] [PATCH 2/5] exec: qemu_ram_alloc_device, qemu_ram_resize

["Michael S. Tsirkin" <mst@redhat.com>]

Add API to manage on-device RAM.
This looks just like regular RAM from migration POV,
but has two special properties internally:

    - it is never exposed to guest
    - block is sized on migration, making it easier to extend
      without breaking migration compatibility or wasting
      virtual memory
    - callers must specify an upper bound on size

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

qemu_ram_alloc_device allocates this memory, qemu_ram_resize resizes it.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/exec/cpu-all.h  |   8 +++-
 include/exec/ram_addr.h |   7 +++
 exec.c                  | 113 +++++++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 115 insertions(+), 13 deletions(-)

diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index 62f5581..26eb9b2 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -299,11 +299,15 @@ CPUArchState *cpu_copy(CPUArchState *env);
 
 /* memory API */
 
-typedef struct RAMBlock {
+typedef struct RAMBlock RAMBlock;
+
+struct RAMBlock {
     struct MemoryRegion *mr;
     uint8_t *host;
     ram_addr_t offset;
     ram_addr_t length;
+    ram_addr_t max_length;
+    void (*resized)(const char*, uint64_t length, void *host);
     uint32_t flags;
     char idstr[256];
     /* Reads can take either the iothread or the ramlist lock.
@@ -311,7 +315,7 @@ typedef struct RAMBlock {
      */
     QTAILQ_ENTRY(RAMBlock) next;
     int fd;
-} RAMBlock;
+};
 
 static inline void *ramblock_ptr(RAMBlock *block, ram_addr_t offset)
 {
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index d7e5238..72ab12b 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -28,12 +28,19 @@ ram_addr_t qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
 ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
                                    MemoryRegion *mr, Error **errp);
 ram_addr_t qemu_ram_alloc(ram_addr_t size, MemoryRegion *mr, Error **errp);
+ram_addr_t qemu_ram_alloc_device(ram_addr_t size, ram_addr_t max_size,
+                                 void (*resized)(const char*,
+                                                 uint64_t length,
+                                                 void *host),
+                                 MemoryRegion *mr, Error **errp);
 int qemu_get_ram_fd(ram_addr_t addr);
 void *qemu_get_ram_block_host_ptr(ram_addr_t addr);
 void *qemu_get_ram_ptr(ram_addr_t addr);
 void qemu_ram_free(ram_addr_t addr);
 void qemu_ram_free_from_ptr(ram_addr_t addr);
 
+int qemu_ram_resize(ram_addr_t base, ram_addr_t newsize, Error **errp);
+
 static inline bool cpu_physical_memory_get_dirty(ram_addr_t start,
                                                  ram_addr_t length,
                                                  unsigned client)
diff --git a/exec.c b/exec.c
index 9648669..a177816 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)
 
+/* On-device RAM allocated with g_malloc: supports realloc,
+ * not accessible to vcpu on kvm.
+ */
+#define RAM_DEVICE     (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 +1301,50 @@ static int memory_try_enable_merging(void *addr, size_t len)
     return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE);
 }
 
+int qemu_ram_resize(ram_addr_t base, ram_addr_t newsize, Error **errp)
+{
+    RAMBlock *block = find_ram_block(base);
+
+    assert(block);
+
+    if (block->length == newsize) {
+        return 0;
+    }
+
+    if (!(block->flags & RAM_DEVICE)) {
+        error_setg_errno(errp, EINVAL,
+                         "Length mismatch: %s: 0x" RAM_ADDR_FMT
+                         " in != 0x" RAM_ADDR_FMT, block->idstr,
+                         newsize, block->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;
+    }
+
+    block->host = g_realloc(block->host, newsize);
+    if (!block->host) {
+        error_setg_errno(errp, errno,
+                         "cannot allocate guest memory '%s'",
+                         memory_region_name(block->mr));
+        return -ENOMEM;
+    }
+
+    cpu_physical_memory_clear_dirty_range_nocode(block->offset, block->length);
+    block->length = newsize;
+    memset(block->host, 0, block->length);
+    cpu_physical_memory_set_dirty_range_nocode(block->offset, block->length);
+    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;
@@ -1308,7 +1357,16 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp)
     new_block->offset = find_ram_offset(new_block->length);
 
     if (!new_block->host) {
-        if (xen_enabled()) {
+        if (new_block->flags & RAM_DEVICE) {
+            new_block->host = g_malloc0(new_block->length);
+            if (!new_block->host) {
+                error_setg_errno(errp, errno,
+                                 "cannot allocate guest memory '%s'",
+                                 memory_region_name(new_block->mr));
+                qemu_mutex_unlock_ramlist();
+                return -1;
+            }
+        } else if (xen_enabled()) {
             xen_ram_alloc(new_block->offset, new_block->length, new_block->mr);
         } else {
             new_block->host = phys_mem_alloc(new_block->length,
@@ -1352,12 +1410,14 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp)
     }
     cpu_physical_memory_set_dirty_range(new_block->offset, new_block->length);
 
-    qemu_ram_setup_dump(new_block->host, new_block->length);
-    qemu_madvise(new_block->host, new_block->length, QEMU_MADV_HUGEPAGE);
-    qemu_madvise(new_block->host, new_block->length, QEMU_MADV_DONTFORK);
+    if (!(new_block->flags & RAM_DEVICE)) {
+        qemu_ram_setup_dump(new_block->host, new_block->length);
+        qemu_madvise(new_block->host, new_block->length, QEMU_MADV_HUGEPAGE);
+        qemu_madvise(new_block->host, new_block->length, QEMU_MADV_DONTFORK);
 
-    if (kvm_enabled()) {
-        kvm_setup_guest_memory(new_block->host, new_block->length);
+        if (kvm_enabled()) {
+            kvm_setup_guest_memory(new_block->host, new_block->length);
+        }
     }
 
     return new_block->offset;
@@ -1392,6 +1452,7 @@ ram_addr_t qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
     new_block = g_malloc0(sizeof(*new_block));
     new_block->mr = mr;
     new_block->length = size;
+    new_block->max_length = size;
     new_block->flags = share ? RAM_SHARED : 0;
     new_block->host = file_ram_alloc(new_block, size,
                                      mem_path, errp);
@@ -1410,7 +1471,12 @@ 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 device,
                                    MemoryRegion *mr, Error **errp)
 {
     RAMBlock *new_block;
@@ -1418,14 +1484,21 @@ 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->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 (device) {
+        new_block->flags |= RAM_DEVICE;
+    }
     addr = ram_block_add(new_block, &local_err);
     if (local_err) {
         g_free(new_block);
@@ -1435,9 +1508,24 @@ 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_device(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)
@@ -1471,6 +1559,8 @@ void qemu_ram_free(ram_addr_t addr)
             ram_list.version++;
             if (block->flags & RAM_PREALLOC) {
                 ;
+            } else if (block->flags & RAM_DEVICE) {
+                g_free(block->host);
             } else if (xen_enabled()) {
                 xen_invalidate_map_cache_entry(block->host);
 #ifndef _WIN32
@@ -1501,7 +1591,8 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
         offset = addr - block->offset;
         if (offset < block->length) {
             vaddr = ramblock_ptr(block, offset);
-            if (block->flags & RAM_PREALLOC) {
+            if (block->flags & RAM_PREALLOC ||
+                block->flags & RAM_DEVICE) {
                 ;
             } else if (xen_enabled()) {
                 abort();
-- 
MST