memory: add RAM_PRIVATE

Define the RAM_PRIVATE flag.

In RAMBlock creation functions, if MAP_SHARED is 0 in the flags parameter,
in a subsequent patch the implementation may still create a shared mapping
if other conditions require it.  Callers who specifically want a private
mapping, eg for objects specified by the user, must pass RAM_PRIVATE.

After RAMBlock creation, MAP_SHARED in the block's flags indicates whether
the block is shared or private, and MAP_PRIVATE is omitted.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-6-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

backends/hostmem-epc.c

@@ -36,7 +36,7 @@ sgx_epc_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 
     backend->aligned = true;
     name = object_get_canonical_path(OBJECT(backend));
-    ram_flags = (backend->share ? RAM_SHARED : 0) | RAM_PROTECTED;
+    ram_flags = (backend->share ? RAM_SHARED : RAM_PRIVATE) | RAM_PROTECTED;
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,
                                           backend->size, ram_flags, fd, 0, errp);
 }

backends/hostmem-file.c

@@ -82,7 +82,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 
     backend->aligned = true;
     name = host_memory_backend_get_name(backend);
-    ram_flags = backend->share ? RAM_SHARED : 0;
+    ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= fb->readonly ? RAM_READONLY_FD : 0;
     ram_flags |= fb->rom == ON_OFF_AUTO_ON ? RAM_READONLY : 0;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;

backends/hostmem-memfd.c

@@ -52,7 +52,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 
     backend->aligned = true;
     name = host_memory_backend_get_name(backend);
-    ram_flags = backend->share ? RAM_SHARED : 0;
+    ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
     ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
     return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name,

backends/hostmem-ram.c

@@ -28,7 +28,7 @@ ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     }
 
     name = host_memory_backend_get_name(backend);
-    ram_flags = backend->share ? RAM_SHARED : 0;
+    ram_flags = backend->share ? RAM_SHARED : RAM_PRIVATE;
     ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
     ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
     return memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend),

include/exec/memory.h

@@ -246,6 +246,16 @@ typedef struct IOMMUTLBEvent {
 /* RAM can be private that has kvm guest memfd backend */
 #define RAM_GUEST_MEMFD   (1 << 12)
 
+/*
+ * In RAMBlock creation functions, if MAP_SHARED is 0 in the flags parameter,
+ * the implementation may still create a shared mapping if other conditions
+ * require it.  Callers who specifically want a private mapping, eg objects
+ * specified by the user, must pass RAM_PRIVATE.
+ * After RAMBlock creation, MAP_SHARED in the block's flags indicates whether
+ * the block is shared or private, and MAP_PRIVATE is omitted.
+ */
+#define RAM_PRIVATE (1 << 13)
+
 static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
                                        IOMMUNotifierFlag flags,
                                        hwaddr start, hwaddr end,

system/physmem.c

@@ -1952,7 +1952,11 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, ram_addr_t max_size,
     ERRP_GUARD();
     RAMBlock *new_block;
     Error *local_err = NULL;
-    int64_t file_size, file_align;
+    int64_t file_size, file_align, share_flags;
+
+    share_flags = ram_flags & (RAM_PRIVATE | RAM_SHARED);
+    assert(share_flags != (RAM_SHARED | RAM_PRIVATE));
+    ram_flags &= ~RAM_PRIVATE;
 
     /* Just support these ram flags by now. */
     assert((ram_flags & ~(RAM_SHARED | RAM_PMEM | RAM_NORESERVE |
@@ -2097,7 +2101,11 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
 {
     RAMBlock *new_block;
     Error *local_err = NULL;
-    int align;
+    int align, share_flags;
+
+    share_flags = ram_flags & (RAM_PRIVATE | RAM_SHARED);
+    assert(share_flags != (RAM_SHARED | RAM_PRIVATE));
+    ram_flags &= ~RAM_PRIVATE;
 
     assert((ram_flags & ~(RAM_SHARED | RAM_RESIZEABLE | RAM_PREALLOC |
                           RAM_NORESERVE | RAM_GUEST_MEMFD)) == 0);
@@ -2172,7 +2180,8 @@ RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
 RAMBlock *qemu_ram_alloc(ram_addr_t size, uint32_t ram_flags,
                          MemoryRegion *mr, Error **errp)
 {
-    assert((ram_flags & ~(RAM_SHARED | RAM_NORESERVE | RAM_GUEST_MEMFD)) == 0);
+    assert((ram_flags & ~(RAM_SHARED | RAM_NORESERVE | RAM_GUEST_MEMFD |
+                          RAM_PRIVATE)) == 0);
     return qemu_ram_alloc_internal(size, size, NULL, NULL, ram_flags, mr, errp);
 }