Since commit 2cdfcf272d ("memory: assign MemoryRegionOps to all
regions"), all newly created regions are assigned with
unassigned_mem_ops (which might be then overwritten).
When using aliased container regions, and there is no region mapped
at address 0 in the container, the memory_region_dispatch_read()
and memory_region_dispatch_write() calls incorrectly return the
container unassigned_mem_ops, because the alias offset is not used.
Consider the following setup:
+--------------------+ < - - - - - - - - - - - +
| Container | mr
| (unassigned_mem) | |
| |
| | |
| | alias_offset
+ + <- - - - - - +----------+---------+
| +----------------+ | | |
| | MemoryRegion0 | | | |
| +----------------+ | | Alias | addr1
| | MemoryRegion1 | | <~ ~ ~ ~ ~ | | <~~~~~~
| +----------------+ | | |
| | +--------------------+
| |
| |
| |
| |
| +----------------+ |
| | MemoryRegionX | |
| +----------------+ |
| | MemoryRegionY | |
| +----------------+ |
| | MemoryRegionZ | |
| +----------------+ |
+--------------------+
The memory_region_init_alias() flow is:
memory_region_init_alias()
-> memory_region_init()
-> object_initialize(TYPE_MEMORY_REGION)
-> memory_region_initfn()
-> mr->ops = &unassigned_mem_ops;
Later when accessing offset=addr1 via the alias, we expect to hit
MemoryRegion1. The memory_region_dispatch_read() flow is:
memory_region_dispatch_read(addr1)
-> memory_region_access_valid(mr) <- addr1 offset is ignored
-> mr->ops->valid.accepts()
-> unassigned_mem_accepts()
<- false
<- false
<- MEMTX_DECODE_ERROR
The caller gets a MEMTX_DECODE_ERROR while the access is OK.
Fix by dispatching aliases recursively, accessing its origin region
after adding the alias offset.
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210418055708.820980-1-f4bug@amsat.org>
1a59bdba4b