Re: [Qemu-devel] [PATCH] numa: set the memory backend "is_mapped" field

[Igor Mammedov]

On Tue, 19 Jul 2016 10:28:35 +0200
Greg Kurz <address@hidden> wrote:

> Commit 2aece63 "hostmem: detect host backend memory is being used properly"
> added a way to know if a memory backend is busy or available for use. It
> caused a slight regression if we pass the same backend to a NUMA node and
> to a pc-dimm device:
> 
> -m 1G,slots=2,maxmem=2G \
> -object memory-backend-ram,size=1G,id=mem-mem1 \
> -device pc-dimm,id=dimm-mem1,memdev=mem-mem1 \
> -numa node,nodeid=0,memdev=mem-mem1
> 
> Before commit 2aece63, this would cause QEMU to print an error message and
> to exit gracefully:
> 
> qemu-system-ppc64: -device pc-dimm,id=dimm-mem1,memdev=mem-mem1:
>     can't use already busy memdev: mem-mem1
> 
> Since commit 2aece63, QEMU hits an assertion in the memory code:
> 
> qemu-system-ppc64: memory.c:1934: memory_region_add_subregion_common:
>     Assertion `!subregion->container' failed.
> Aborted
> 
> This happens because pc-dimm devices don't use memory_region_is_mapped()
> anymore and cannot guess the backend is already used by a NUMA node.
> 
> Let's revert to the previous behavior by turning the NUMA code to also
> call host_memory_backend_set_mapped() when it uses a backend.
> 
> Fixes: 2aece63c8a9d2c3a8ff41d2febc4cdeff2633331
> Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Igor Mammedov <address@hidden>

> ---
>  numa.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/numa.c b/numa.c
> index cbae430e3644..72861713e5fd 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -463,6 +463,7 @@ void memory_region_allocate_system_memory(MemoryRegion 
> *mr, Object *owner,
>              exit(1);
>          }
>  
> +        host_memory_backend_set_mapped(backend, true);
>          memory_region_add_subregion(mr, addr, seg);
>          vmstate_register_ram_global(seg);
>          addr += size;
> 
>