[Qemu-devel] [RFC 1/4] Allocate non-RAM MemoryRegion from user pointer

[Alvise Rigo]

The method memory_region_init_ptr() allows the allocation of non-RAM
memory from a user-provided pointer. The function is useful in VFIO,
where a pointer to the memory regions of the device is provided by
the user.

A new flag inside MemoryRegion tells if the memory has been allocated
through a user pointer, allowing to not call the IOMMU callbacks for
these regions, but rather to access the memory directly.

Signed-off-by: Alvise Rigo <address@hidden>
---
 exec.c                |  2 +-
 include/exec/memory.h | 16 ++++++++++++++++
 memory.c              | 14 ++++++++++++++
 memory_mapping.c      |  2 +-
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/exec.c b/exec.c
index 91513c6..ed91823 100644
--- a/exec.c
+++ b/exec.c
@@ -341,7 +341,7 @@ address_space_translate_internal(AddressSpaceDispatch *d, 
hwaddr addr, hwaddr *x
 
 static inline bool memory_access_is_direct(MemoryRegion *mr, bool is_write)
 {
-    if (memory_region_is_ram(mr)) {
+    if (memory_region_is_ram(mr) || mr->alloc_from_ptr) {
         return !(is_write && mr->readonly);
     }
     if (memory_region_is_romd(mr)) {
diff --git a/include/exec/memory.h b/include/exec/memory.h
index c084db2..1f2745d 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -149,6 +149,7 @@ struct MemoryRegion {
     bool rom_device;
     bool warning_printed; /* For reservations */
     bool flush_coalesced_mmio;
+    bool alloc_from_ptr;
     MemoryRegion *alias;
     hwaddr alias_offset;
     int priority;
@@ -327,6 +328,21 @@ void memory_region_init_ram_ptr(MemoryRegion *mr,
                                 const char *name,
                                 uint64_t size,
                                 void *ptr);
+/**
+ * memory_region_init_ram_ptr:  As before, but for non-RAM memory.
+ *
+ * @mr: the #MemoryRegion to be initialized.
+ * @owner: the object that tracks the region's reference count
+ * @name: the name of the region.
+ * @size: size of the region.
+ * @ptr: memory to be mapped; must contain at least @size bytes.
+ */
+void memory_region_init_ptr(MemoryRegion *mr,
+                            struct Object *owner,
+                            const char *name,
+                            uint64_t size,
+                            void *ptr);
+
 
 /**
  * memory_region_init_alias: Initialize a memory region that aliases all or a
diff --git a/memory.c b/memory.c
index 3f1df23..fbb48bf 100644
--- a/memory.c
+++ b/memory.c
@@ -1030,6 +1030,20 @@ void memory_region_init_ram_ptr(MemoryRegion *mr,
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram_from_ptr;
     mr->ram_addr = qemu_ram_alloc_from_ptr(size, ptr, mr);
+    mr->alloc_from_ptr = true;
+}
+
+void memory_region_init_ptr(MemoryRegion *mr,
+                                Object *owner,
+                                const char *name,
+                                uint64_t size,
+                                void *ptr)
+{
+    memory_region_init(mr, owner, name, size);
+    mr->terminates = true;
+    mr->destructor = memory_region_destructor_ram_from_ptr;
+    mr->ram_addr = qemu_ram_alloc_from_ptr(size, ptr, mr);
+    mr->alloc_from_ptr = true;
 }
 
 void memory_region_init_alias(MemoryRegion *mr,
diff --git a/memory_mapping.c b/memory_mapping.c
index 87a6ed5..6e3d334 100644
--- a/memory_mapping.c
+++ b/memory_mapping.c
@@ -203,7 +203,7 @@ static void guest_phys_blocks_region_add(MemoryListener 
*listener,
     GuestPhysBlock *predecessor;
 
     /* we only care about RAM */
-    if (!memory_region_is_ram(section->mr)) {
+    if (!memory_region_is_ram(section->mr) && !section->mr->alloc_from_ptr) {
         return;
     }
 
-- 
1.8.3.2