On Tue, 7 Jun 2016 22:29:30 -0600 Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Wed, 8 Jun 2016 11:18:42 +0800 > Dong Jia <bjsdjshi@xxxxxxxxxxxxxxxxxx> wrote: > > > On Tue, 7 Jun 2016 19:39:21 -0600 > > Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > > > > > On Wed, 8 Jun 2016 01:18:42 +0000 > > > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > > > > > > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > > > > Sent: Wednesday, June 08, 2016 6:42 AM > > > > > > > > > > On Tue, 7 Jun 2016 03:03:32 +0000 > > > > > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > > > > > > > > > > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > > > > > > Sent: Tuesday, June 07, 2016 3:31 AM > > > > > > > > > > > > > > On Mon, 6 Jun 2016 10:44:25 -0700 > > > > > > > Neo Jia <cjia@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > On Mon, Jun 06, 2016 at 04:29:11PM +0800, Dong Jia wrote: > > > > > > > > > On Sun, 5 Jun 2016 23:27:42 -0700 > > > > > > > > > Neo Jia <cjia@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > 2. VFIO_DEVICE_CCW_CMD_REQUEST > > > > > > > > > This intends to handle an intercepted channel I/O instruction. It > > > > > > > > > basically need to do the following thing: > > > > > > > > > > > > > > > > May I ask how and when QEMU knows that he needs to issue such VFIO ioctl at > > > > > > > > first place? > > > > > > > > > > > > > > Yep, this is my question as well. It sounds a bit like there's an > > > > > > > emulated device in QEMU that's trying to tell the mediated device when > > > > > > > to start an operation when we probably should be passing through > > > > > > > whatever i/o operations indicate that status directly to the mediated > > > > > > > device. Thanks, > > > > > > > > > > > > > > Alex > > > > > > > > > > > > Below is copied from Dong's earlier post which said clear that > > > > > > a guest cmd submission will trigger the whole flow: > > > > > > > > > > > > ---- > > > > > > Explanation: > > > > > > Q1-Q4: Qemu side process. > > > > > > K1-K6: Kernel side process. > > > > > > > > > > > > Q1. Intercept a ssch instruction. > > > > > > Q2. Translate the guest ccw program to a user space ccw program > > > > > > (u_ccwchain). > > > > > > Q3. Call VFIO_DEVICE_CCW_CMD_REQUEST (u_ccwchain, orb, irb). > > > > > > K1. Copy from u_ccwchain to kernel (k_ccwchain). > > > > > > K2. Translate the user space ccw program to a kernel space ccw > > > > > > program, which becomes runnable for a real device. > > > > > > K3. With the necessary information contained in the orb passed in > > > > > > by Qemu, issue the k_ccwchain to the device, and wait event q > > > > > > for the I/O result. > > > > > > K4. Interrupt handler gets the I/O result, and wakes up the wait q. > > > > > > K5. CMD_REQUEST ioctl gets the I/O result, and uses the result to > > > > > > update the user space irb. > > > > > > K6. Copy irb and scsw back to user space. > > > > > > Q4. Update the irb for the guest. > > > > > > ---- > > > > > > > > > > Right, but this was the pre-mediated device approach, now we no longer > > > > > need step Q2 so we really only need Q1 and therefore Q3 to exist in > > > > > QEMU if those are operations that are not visible to the mediated > > > > > device; which they very well might be, since it's described as an > > > > > instruction rather than an i/o operation. It's not terrible if that's > > > > > the case, vfio-pci has its own ioctl for doing a hot reset. > > Dear Alex, Kevin and Neo, > > > > 'ssch' is a privileged I/O instruction, which should be finally issued > > to the dedicated subchannel of the physical device. > > > > BTW, I did remove step Q2 with all of the user-space translation code, > > according to your comments in another thread. > > > > > > > > > > > > > > > > > > > > > My understanding is that such thing belongs to how device is mediated > > > > > > (so device driver specific), instead of something to be abstracted in > > > > > > VFIO which manages resource but doesn't care how resource is used. > > > > > > > > > > > > Actually we have same requirement in vGPU case, that a guest driver > > > > > > needs submit GPU commands through some MMIO register. vGPU device > > > > > > model will intercept the submission request (in its own way), do its > > > > > > necessary scan/audit to ensure correctness/security, and then submit > > > > > > to physical GPU through vendor specific interface. > > > > > > > > > > > > No difference with channel I/O here. > > > > > > > > > > Well, if the GPU command is submitted through an MMIO register, is that > > > > > MMIO register part of the mediated device? If so, could the mediated > > > > > device recognize the command and do the scan/audit itself? QEMU must > > > > > not be the point at which mediation occurs for security purposes, QEMU > > > > > is userspace and userspace is not to be trusted. I'm still open to > > > > > ioctls where it makes sense, as above, we have PCI specific ioctls and > > > > > already, but we need to evaluate each one, why it needs to exist, and > > > > > whether we can skip it if the mediated device can trigger the action on > > > > > its own. After all, that's why we're using the vfio api, so we can > > > > > re-use much of the existing infrastructure, especially for a vGPU that > > > > > exposes itself as a PCI device. Thanks, > > > > > > > > > > > > > My point is that a guest submission on vGPU is just a normal trapped > > > > register write, which is forwarded from Qemu to VFIO through pwrite > > > > interface and then hit mediated vGPU device. The mediated device > > > > will recognize this register write as a submission request and then do > > > > necessary scan (looks we are saying same thing) and then submit to > > > > physical device driver. If loading ccw cmds on channel i/o are also > > > > through some I/O registers, it can be implemented same way w/o > > > > introducing new ioctl. > > We are different here. The target of an I/O instruction is the > > subchannel. CCW devices don't have these kind of registers. The mediated > > ccw device can not recognize such an submission by its own capbilities. > > > > A CCW device does not have such registers in both the physical and the > > mediated devices to sense or recognize the submission request. It's the > > CPU that recognizes the submission by intercepting the guest ssch > > instruction. > > > > CPU can not tell if it is issued from a passed thru device driver or a > > virtio device driver from the guest. So it has to exit to QEMU, and let > > QEMU take over. > > > > Once QEMU identifies the target subchannel is serving a passed thru > > device, it uses the ioctl to pass the instruction parameters into the > > kernel all the way along the mediated driver to the physical driver to > > the subchannel to perform the I/O operation. > > > > > > The r/w handler of mediated device can figure > > > > out whether it's a ccw submission or not. But my understanding might > > > > be wrong here. > > We don't have registers to sense an instruction or operation. > > Ok, so it seems we need to create some sort of interface to initiate > the ccw program, but I suppose I'm not yet convinced that it needs a > new ioctl. For instance if you only need to "kick" the device to tell > it when to begin translation and execution, we could create a virtual > interrupt into the mediated device with an irqfd. QEMU writes to the > irqfd (eventfd), the mediated driver receives this kick and begins > processing. Another virtual interrupt out to the user might indicate > completion. On the other hand if the ioctl was intended to write the > ccw program itself to the device, we have vfio device regions that can > do this. Simply define within the vfio-ccw API that one of the regions > is a virtual program buffer and define the API between the mediated > driver and user the sequence of writes that load the program state, > initiate the program, and return the result. > > The vfio API already has a very extensible mechanism for communicating > with a device through regions and interrupts, not all of which > necessarily need to match physical attributes of the device. ioctls > can be added, but lets exhaust the mechanisms we already have through > the vfio api first. Thanks, Dear Alex and Neo, I tried as what you suggested - add an MMIO region to the device, and it works fine. It's an interesting and elegant way. I like it. :> So indeed, we neither need to introduce a new ioctl command, nor the ioctl callback on phy_device_ops. Thanks! > > Alex > -------- Dong Jia -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
