vhost-user: fix regions provied with VHOST_USER_SET_MEM_TABLE message

Old code was affected by memory gaps which resulted in buffer pointers
pointing to address outside of the mapped regions.

Here we are introducing following changes:
 - new function qemu_get_ram_block_host_ptr() returns host pointer
   to the ram block, it is needed to calculate offset of specific
   region in the host memory
 - new field mmap_offset is added to the VhostUserMemoryRegion. It
   contains offset where specific region starts in the mapped memory.
   As there is stil no wider adoption of vhost-user agreement was made
   that we will not bump version number due to this change
 - other fileds in VhostUserMemoryRegion struct are not changed, as
   they are all needed for usermode app implementation
 - region data is not taken from ram_list.blocks anymore, instead we
   use region data which is alredy calculated for use in vhost-net
 - Now multiple regions can have same FD and user applicaton can call
   mmap() multiple times with the same FD but with different offset
   (user needs to take care for offset page alignment)

Signed-off-by: Damjan Marion <damarion@cisco.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Damjan Marion <damarion@cisco.com>

docs/specs/vhost-user.txt

@@ -78,13 +78,14 @@ Depending on the request type, payload can be:
    Padding: 32-bit
 
    A region is:
-   ---------------------------------------
-   | guest address | size | user address |
-   ---------------------------------------
+   -----------------------------------------------------
+   | guest address | size | user address | mmap offset |
+   -----------------------------------------------------
 
    Guest address: a 64-bit guest address of the region
    Size: a 64-bit size
    User address: a 64-bit user address
+   mmmap offset: 64-bit offset where region starts in the mapped memory
 
 
 In QEMU the vhost-user message is implemented with the following struct:

exec.c

@@ -1456,6 +1456,13 @@ int qemu_get_ram_fd(ram_addr_t addr)
     return block->fd;
 }
 
+void *qemu_get_ram_block_host_ptr(ram_addr_t addr)
+{
+    RAMBlock *block = qemu_get_ram_block(addr);
+
+    return block->host;
+}
+
 /* Return a host pointer to ram allocated with qemu_ram_alloc.
    With the exception of the softmmu code in this file, this should
    only be used for local memory (e.g. video ram) that the device owns,

hw/virtio/vhost-user.c

@@ -14,6 +14,7 @@
 #include "sysemu/kvm.h"
 #include "qemu/error-report.h"
 #include "qemu/sockets.h"
+#include "exec/ram_addr.h"
 
 #include <fcntl.h>
 #include <unistd.h>
@@ -47,6 +48,7 @@ typedef struct VhostUserMemoryRegion {
     uint64_t guest_phys_addr;
     uint64_t memory_size;
     uint64_t userspace_addr;
+    uint64_t mmap_offset;
 } VhostUserMemoryRegion;
 
 typedef struct VhostUserMemory {
@@ -183,10 +185,10 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
 {
     VhostUserMsg msg;
     VhostUserRequest msg_request;
-    RAMBlock *block = 0;
     struct vhost_vring_file *file = 0;
     int need_reply = 0;
     int fds[VHOST_MEMORY_MAX_NREGIONS];
+    int i, fd;
     size_t fd_num = 0;
 
     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
@@ -212,14 +214,17 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
         break;
 
     case VHOST_SET_MEM_TABLE:
-        QTAILQ_FOREACH(block, &ram_list.blocks, next)
-        {
-            if (block->fd > 0) {
-                msg.memory.regions[fd_num].userspace_addr =
-                    (uintptr_t) block->host;
-                msg.memory.regions[fd_num].memory_size = block->length;
-                msg.memory.regions[fd_num].guest_phys_addr = block->offset;
-                fds[fd_num++] = block->fd;
+        for (i = 0; i < dev->mem->nregions; ++i) {
+            struct vhost_memory_region *reg = dev->mem->regions + i;
+            fd = qemu_get_ram_fd(reg->guest_phys_addr);
+            if (fd > 0) {
+                msg.memory.regions[fd_num].userspace_addr = reg->userspace_addr;
+                msg.memory.regions[fd_num].memory_size  = reg->memory_size;
+                msg.memory.regions[fd_num].guest_phys_addr = reg->guest_phys_addr;
+                msg.memory.regions[fd_num].mmap_offset = reg->userspace_addr -
+                    (uintptr_t) qemu_get_ram_block_host_ptr(reg->guest_phys_addr);
+                assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
+                fds[fd_num++] = fd;
             }
         }
 

include/exec/ram_addr.h

@@ -29,6 +29,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
                                    MemoryRegion *mr);
 ram_addr_t qemu_ram_alloc(ram_addr_t size, MemoryRegion *mr);
 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);