On Mon, Jun 08, 2020 at 09:17:45AM +0200, David Hildenbrand wrote: > On 08.06.20 09:08, Michael S. Tsirkin wrote: > > On Mon, Jun 08, 2020 at 08:58:31AM +0200, David Hildenbrand wrote: > >> On 08.06.20 08:14, Michael S. Tsirkin wrote: > >>> If subblock size is large (e.g. 1G) 32 bit math involving it > >>> can overflow. Rather than try to catch all instances of that, > >>> let's tweak block size to 64 bit. > >> > >> I fail to see where we could actually trigger an overflow. The reported > >> warning looked like a false positive to me. > > > > > > So > > > > const uint64_t size = count * vm->subblock_size; > > > > is it unreasonable for count to be 4K with subblock_size being 1M? > > virtio_mem_mb_plug_sb() and friends are only called on subblocks > residing within a single Linux memory block. (currently, 128MB .. 2G on > x86-64). A subblock on x86-64 is currently at least 4MB. > > So "count * vm->subblock_size" can currently not exceed the Linux memory > block size (in practice, it is max 128MB). > > > > >>> > >>> It ripples through UAPI which is an ABI change, but it's not too late to > >>> make it, and it will allow supporting >4Gbyte blocks while might > >>> become necessary down the road. > >>> > >> > >> This might break cloud-hypervisor, who's already implementing this > >> protocol upstream (ccing Hui). > >> https://github.com/cloud-hypervisor/cloud-hypervisor/blob/master/vm-virtio/src/mem.rs > >> > >> (blocks in the gigabyte range were never the original intention of > >> virtio-mem, but I am not completely opposed to that) > > > > > > So in that case, can you code up validation in the probe function? > > If we would currently have a "block_size" > Linux memory block size, we > bail out. > > virtio_mem_init(): > > if (vm->device_block_size > memory_block_size_bytes()) { > dev_err(&vm->vdev->dev, > "The block size is not supported (too big).\n"); > return -EINVAL; > } Sounds good. > So what's reported can currently not happen. Having that said, changing > "subblock_size" to be an uint64_t is a good cleanup, especially for the > future. OK, no need to argue about it then. I tweaked the subject as you suggested and queued it then. > > > > -- > Thanks, > > David / dhildenb _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
