On Tue, Nov 19, 2019 at 09:46:53PM -0400, Jason Gunthorpe wrote: > On Tue, Nov 19, 2019 at 07:16:21PM -0500, Michael S. Tsirkin wrote: > > On Tue, Nov 19, 2019 at 07:10:23PM -0400, Jason Gunthorpe wrote: > > > On Tue, Nov 19, 2019 at 04:33:40PM -0500, Michael S. Tsirkin wrote: > > > > On Tue, Nov 19, 2019 at 03:15:47PM -0400, Jason Gunthorpe wrote: > > > > > On Tue, Nov 19, 2019 at 01:58:42PM -0500, Michael S. Tsirkin wrote: > > > > > > On Tue, Nov 19, 2019 at 12:46:32PM -0400, Jason Gunthorpe wrote: > > > > > > > As always, this is all very hard to tell without actually seeing real > > > > > > > accelerated drivers implement this. > > > > > > > > > > > > > > Your patch series might be a bit premature in this regard. > > > > > > > > > > > > Actually drivers implementing this have been posted, haven't they? > > > > > > See e.g. https://lwn.net/Articles/804379/ > > > > > > > > > > Is that a real driver? It looks like another example quality > > > > > thing. > > > > > > > > > > For instance why do we need any of this if it has '#define > > > > > IFCVF_MDEV_LIMIT 1' ? > > > > > > > > > > Surely for this HW just use vfio over the entire PCI function and be > > > > > done with it? > > > > > > > > What this does is allow using it with unmodified virtio drivers > > > > within guests. You won't get this with passthrough as it only > > > > implements parts of virtio in hardware. > > > > > > I don't mean use vfio to perform passthrough, I mean to use vfio to > > > implement the software parts in userspace while vfio to talk to the > > > hardware. > > > > You repeated vfio twice here, hard to decode what you meant actually. > > 'while using vifo to talk to the hardware' Sorry still have trouble reading that. > > > kernel -> vfio -> user space virtio driver -> qemu -> guest > > > > Exactly what has been implemented for control path. > > I do not mean the modified mediated vfio this series proposes, I mean > vfio-pci, on a full PCI VF, exactly like we have today. > > > The interface between vfio and userspace is > > based on virtio which is IMHO much better than > > a vendor specific one. userspace stays vendor agnostic. > > Why is that even a good thing? It is much easier to provide drivers > via qemu/etc in user space then it is to make kernel upgrades. We've > learned this lesson many times. > > This is why we have had the philosophy that if it doesn't need to be > in the kernel it should be in userspace. > > > > Generally we don't want to see things in the kernel that can be done > > > in userspace, and to me, at least for this driver, this looks > > > completely solvable in userspace. > > > > I don't think that extends as far as actively encouraging userspace > > drivers poking at hardware in a vendor specific way. > > Yes, it does, if you can implement your user space requirements using > vfio then why do you need a kernel driver? People's requirements differ. You are happy with just pass through a VF you can already use it. Case closed. There are enough people who have a fixed userspace that people have built virtio accelerators, now there's value in supporting that, and a vendor specific userspace blob is not supporting that requirement. > The kernel needs to be involved when there are things only the kernel > can do. If IFC has such things they should be spelled out to justify > using a mediated device. > > > That has lots of security and portability implications and isn't > > appropriate for everyone. > > This is already using vfio. It's using the IOMMU parts since these are portable. But the userspace interface is vendor-independent here. > It doesn't make sense to claim that using > vfio properly is somehow less secure or less portable. > > What I find particularly ugly is that this 'IFC VF NIC' driver > pretends to be a mediated vfio device, but actually bypasses all the > mediated device ops for managing dma security and just directly plugs > the system IOMMU for the underlying PCI device into vfio. > > I suppose this little hack is what is motivating this abuse of vfio in > the first place? > > Frankly I think a kernel driver touching a PCI function for which vfio > is now controlling the system iommu for is a violation of the security > model, and I'm very surprised AlexW didn't NAK this idea. > > Perhaps it is because none of the patches actually describe how the > DMA security model for this so-called mediated device works? :( That can be improved, good point. > Or perhaps it is because this submission is split up so much it is > hard to see what is being proposed? (I note this IFC driver is the > first user of the mdev_set_iommu_device() function) I agree it's hard, but then 3 people seem to work on that at the same time. > > It is kernel's job to abstract hardware away and present a unified > > interface as far as possible. > > Sure, you could create a virtio accelerator driver framework in our > new drivers/accel I hear was started. That could make some sense, if > we had HW that actually required/benefited from kernel involvement. > > Jason
