Re: [Qemu-devel] [PATCH v1 1/2] memory-device: turn alignment assert into check

[Igor Mammedov <imammedo@redhat.com>]

On Thu,  7 Jun 2018 17:47:04 +0200
David Hildenbrand <david@redhat.com> wrote:

> The start of the address space indicates which maximum alignment is
> supported by our machine (e.g. ppc, x86 1GB). This is helpful to
> catch fragmenting guest physical memory in strange fashions.
> 
> Right now we can crash QEMU by e.g. (there might be easier examples)
> 
> qemu-system-x86_64 -m 256M,maxmem=20G,slots=2 \
>  -object memory-backend-file,id=mem0,size=8192M,mem-path=/dev/zero,align=8192M \
>  -device pc-dimm,id=dimm1,memdev=mem0
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  hw/mem/memory-device.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
> index 3e04f3954e..6de4f70bb4 100644
> --- a/hw/mem/memory-device.c
> +++ b/hw/mem/memory-device.c
> @@ -116,9 +116,15 @@ uint64_t memory_device_get_free_addr(MachineState *ms, const uint64_t *hint,
>      address_space_start = ms->device_memory->base;
>      address_space_end = address_space_start +
>                          memory_region_size(&ms->device_memory->mr);
> -    g_assert(QEMU_ALIGN_UP(address_space_start, align) == address_space_start);
>      g_assert(address_space_end >= address_space_start);
>  
> +    /* address_space_start indicates the maximum alignment we expect */
> +    if (QEMU_ALIGN_UP(address_space_start, align) != address_space_start) {
> +        error_setg(errp, "the alignment (0%" PRIx64 ") is not supported",
> +                   align);
> +        return 0;
> +    }
> +
>      memory_device_check_addable(ms, size, errp);
>      if (*errp) {
>          return 0;