Re: [PATCH v2] memory: Directly dispatch alias accesses on origin memory region

[Richard Henderson]

On 8/22/20 9:14 AM, Philippe Mathieu-Daudé wrote:
> There is an issue when accessing an alias memory region via the
> memory_region_dispatch_read() / memory_region_dispatch_write()
> calls.
> 
> Since commit 2cdfcf272d ("memory: assign MemoryRegionOps to all
> regions") we assign &unassigned_mem_ops to all MemoryRegions.
> 
> 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;
> 
> When accessing the alias using memory_region_dispatch_read(),
> flow is:
> 
>   memory_region_dispatch_read()
>   -> memory_region_access_valid(mr)
>      -> 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 directly dispatching aliases accesses to its origin region.
> 
> Fixes: 2cdfcf272d ("memory: assign MemoryRegionOps to all regions")
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> Since v1:
> - reword as not a bugfix (Paolo)
> - access the aliases recursively (Paolo)
> ---
>  softmmu/memory.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~