Re: [PATCH v1] virtio-mem: fix division by zero in virtio_mem_activate_memslots_to_plug()

[David Hildenbrand]

On 23.10.23 13:13, David Hildenbrand wrote:
> When running with "dynamic-memslots=off", we enter
> virtio_mem_activate_memslots_to_plug() to return immediately again
> because "vmem->dynamic_memslots == false". However, the compiler might
> not optimize out calculating start_idx+end_idx, where we divide by
> vmem->memslot_size. In such a configuration, the memslot size is 0 and
> we'll get a division by zero:
>
>      (qemu) qom-set vmem0 requested-size 3G
>      (qemu) q35.sh: line 38: 622940 Floating point exception(core dumped)
>
> The same is true for virtio_mem_deactivate_unplugged_memslots(), however
> we never really reach that code without a prior
> virtio_mem_activate_memslots_to_plug() call.
>
> Let's fix it by simply calling these functions only with
> "dynamic-memslots=on".
>
> This was found when using a debug build of QEMU.
>
> Reprted-by: Mario Casquero <mcasquer@redhat.com>
> Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via multiple 
> memslots if enabled")
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---

Queued to

https://github.com/davidhildenbrand/qemu.git mem-next

--
Cheers,

David / dhildenb