Messages in this thread | | | Subject | Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver. | From | Dave Jiang <> | Date | Fri, 8 May 2020 16:52:57 -0700 |
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On 5/8/2020 4:16 PM, Jason Gunthorpe wrote: > On Fri, May 08, 2020 at 01:47:10PM -0700, Raj, Ashok wrote: > >> Even when uaccel was under development, one of the options >> was to use VFIO as the transport, goal was the same i.e to keep >> the user space have one interface. > > I feel a bit out of the loop here, uaccel isn't in today's kernel is > it? I've heard about it for a while, it sounds very similar to RDMA, > so I hope they took some of my advice...
It went into 5.7 kernel. drivers/misc/uacce. It looks char device exported with SVM support.
> >> But the needs of generic user space application is significantly >> different from exporting a more functional device model to guest, >> which isn't full emulated device. which is why VFIO didn't make >> sense for native use. > > I'm not sure this is true. We've done these kinds of emulated SIOV > like things already and there is a huge overlap between what a generic > user application needs and what the VMM neds. Actually almost a > perfect subset except for interrupt remapping (which is quite > trivial). > > The things vfio focuses on, like groups and managing a real config > space just don't apply here. > >> And when we move things from VFIO which is already established >> as a general device model and accepted by multiple VMM's it gives >> instant footing without a whole redesign. > > Yes, I understand, but I think you need to get more people to support > this idea. From my standpoint this is taking secure lean VMMs and > putting emulation code back into them, except in a more dangerous > kernel location. This does not seem like a net win to me. > > You'd be much better to have some userspace library scheme instead of > being completely tied to a kernel interface for modularity. > >> When we move things from VFIO to uaccel to bolt on the functionality >> like VFIO, I suspect we would be moving code/functionality from VFIO >> to Uaccel. I don't know what the net gain would be. > > Most of VFIO functionality is already decomposed inside the kernel, > and you need most of it to do secure user access anyhow. > >> For mdev, would you agree we can keep the current architecture, >> and investigate moving some emulation code to user space (say even for >> standard vfio_pci) and then expand scope later. > > I won't hard NAK this, but I think you need more people to support > this general idea of more emulation code in the kernel to go ahead - > particularly since this is one of many future drivers along this > design. > > It would be good to hear from the VMM teams that this is what they > want (and why), for instance. > > Jason >
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