I am attaching a ramblock device to the guest machine as a
normal block device and trying to write from the guest machine
to host's ramblock device. Block device is attached using Virtio
using following command:
``` qemu-system-x86_64 -enable-kvm -machine type=pc,accel=kvm -cpu host smp 1 -nographic -k de -m 1024 ubuntu16.04.qcow2 -drive if=none,id=drive0,file=/dev/ram -device virtio-blk pci,physical_block_size=4096,logical_block_size=4096,drive=drive0```
Looks like these writes from Guest to host's RAM using Virtio is very slow
(slow like writing to a SSD). What could be the reason for that? Does a
write on a virtualized blkdev will result in a VMEXIT? If not, does it will be
"zero-copy"? What am I missing here? Any pointers on this is greatly appreciated.
Thanks in advance.