On Tue, Apr 10, 2018 at 03:25:45PM +0800, Jason Wang wrote:
To be frank kernel is exactly where device drivers belong. DPDK didI don't object but we need to figure out the advantages of doing it in qemuI'm not quite sure. Do you think it's acceptable toOne problem is that, different virtio ring compatible devicesSo you just move the abstraction layer from qemu to kernel, and you still
may have different device interfaces. That is to say, we will
need different drivers in QEMU. It could be troublesome. And
that's what this patch trying to fix. The idea behind this
patch is very simple: mdev is a standard way to emulate device
in kernel.
need different drivers in kernel for different device interfaces of
accelerators. This looks even more complex than leaving it in qemu. As you
said, another idea is to implement userspace vhost backend for accelerators
which seems easier and could co-work with other parts of qemu without
inventing new type of messages.
add various vendor specific hardware drivers in QEMU?
too.
Thanks
move them to userspace but that's merely a requirement for data path.
*If* you can have them in kernel that is best:
- update kernel and there's no need to rebuild userspace
- apps can be written in any language no need to maintain multiple
libraries or add wrappers
- security concerns are much smaller (ok people are trying to
raise the bar with IOMMUs and such, but it's already pretty
good even without)
The biggest issue is that you let userspace poke at the
device which is also allowed by the IOMMU to poke at
kernel memory (needed for kernel driver to work).
Yes, maybe if device is not buggy it's all fine, but
it's better if we do not have to trust the device
otherwise the security picture becomes more murky.
I suggested attaching a PASID to (some) queues - see my old post "using
PASIDs to enable a safe variant of direct ring access".
Then using IOMMU with VFIO to limit access through queue to corrent
ranges of memory.