This patch has been successfully tested by QE. With a debug QEMU
build, start a VM with a virtio-mem device and 'dynamic-memslots=off',
this one can be resized seamlessly, no floating point exception found.
Tested-by: Mario Casquero <mcasq...@redhat.com>
On Mon, Oct 23, 2023 at 1:13 PM David Hildenbrand <da...@redhat.com> 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 <mcasq...@redhat.com>
> Fixes: 177f9b1ee464 ("virtio-mem: Expose device memory dynamically via
> multiple memslots if enabled")
> Cc: Michael S. Tsirkin <m...@redhat.com>
> Cc: Maciej S. Szmigiero <maciej.szmigi...@oracle.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> hw/virtio/virtio-mem.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index 9dc3c61b5a..be4b0b364f 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -525,9 +525,7 @@ static void
> virtio_mem_activate_memslots_to_plug(VirtIOMEM *vmem,
> vmem->memslot_size;
> unsigned int idx;
>
> - if (!vmem->dynamic_memslots) {
> - return;
> - }
> + assert(vmem->dynamic_memslots);
>
> /* Activate all involved memslots in a single transaction. */
> memory_region_transaction_begin();
> @@ -547,9 +545,7 @@ static void
> virtio_mem_deactivate_unplugged_memslots(VirtIOMEM *vmem,
> vmem->memslot_size;
> unsigned int idx;
>
> - if (!vmem->dynamic_memslots) {
> - return;
> - }
> + assert(vmem->dynamic_memslots);
>
> /* Deactivate all memslots with unplugged blocks in a single
> transaction. */
> memory_region_transaction_begin();
> @@ -598,7 +594,9 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem,
> uint64_t start_gpa,
> virtio_mem_notify_unplug(vmem, offset, size);
> virtio_mem_set_range_unplugged(vmem, start_gpa, size);
> /* Deactivate completely unplugged memslots after updating the
> state. */
> - virtio_mem_deactivate_unplugged_memslots(vmem, offset, size);
> + if (vmem->dynamic_memslots) {
> + virtio_mem_deactivate_unplugged_memslots(vmem, offset, size);
> + }
> return 0;
> }
>
> @@ -635,9 +633,11 @@ static int virtio_mem_set_block_state(VirtIOMEM *vmem,
> uint64_t start_gpa,
> * blocks we are plugging here. The following notification will
> inform
> * registered listeners about the blocks we're plugging.
> */
> - virtio_mem_activate_memslots_to_plug(vmem, offset, size);
> + if (vmem->dynamic_memslots) {
> + virtio_mem_activate_memslots_to_plug(vmem, offset, size);
> + }
> ret = virtio_mem_notify_plug(vmem, offset, size);
> - if (ret) {
> + if (ret && vmem->dynamic_memslots) {
> virtio_mem_deactivate_unplugged_memslots(vmem, offset, size);
> }
> }
> @@ -749,7 +749,9 @@ static int virtio_mem_unplug_all(VirtIOMEM *vmem)
> notifier_list_notify(&vmem->size_change_notifiers, &vmem->size);
>
> /* Deactivate all memslots after updating the state. */
> - virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size);
> + if (vmem->dynamic_memslots) {
> + virtio_mem_deactivate_unplugged_memslots(vmem, 0, region_size);
> + }
> }
>
> trace_virtio_mem_unplugged_all();
> --
> 2.41.0
>
