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 >