On Mon, Apr 13, 2020 at 8:36 AM Alex Williamson <alex.william...@redhat.com> wrote:
> On Sun, 12 Apr 2020 09:10:49 -0700 > Ravi Kerur <rke...@gmail.com> wrote: > > > Hi, > > > > I use Intel NICs for PF and VF devices. VFs are assigned to virtual > > machines and PF is used on the Host. I have intel-iommu=on on GRUB which > > enables DMAR and IOMMU capabilities (checked via 'dmesg | grep -e IOMMU > -e > > DMAR) and use DPDK for datapath acceleration. > > > > Couple of clarifications I need in terms of vfio-pci driver usage > > > > (1) with intel-iommu=pt (Passthrough mode), PF device on host can bind to > > either igb_uio or vfio-pci driver and similarly VF devices assigned to > each > > VM can bind to either igb_uio or vfio-pci driver via Qemu > > Note that the actual option is 'intel_iommu=on iommu=pt'. > My mistake, > > > (2) with intel-iommu=on (IOMMU enabled), PF device on host must bind to > > vfio-pci driver and similarly VF devices assigned to each VM much bind to > > vfio-pci driver. When IOMMU is enabled, only vfio-pci should be used? > > When an IOMMU is present, we refer to the address space through which a > device performs DMA as the I/O Virtual Address space, or IOVA. When > the IOMMU is in passthrough mode, we effectively create an identity > mapping of physical addresses through the IOVA space. Therefore to > program a device to perform a DMA to user memory, the user only needs > to perform a virtual to physical translation on the address and the > device can DMA directly with that physical address thanks to the > identity map. When we're not in passthrough mode, we need to actually > create a mapping through the IOMMU to allow the device to access that > physical memory. VFIO is the only userspace driver interface that I'm > aware of that provides this latter functionality. Therefore, yes, if > you have the IOMMU enabled and not in passthrough mode, your userspace > driver needs support for programming the IOMMU, which vfio-pci provides. > > Also, having both the PF and VFs owned by userspace drivers presents > some additional risks, for example the PF may have access to the data > accessed by the VF, or at least be able to deny service to the VF. > There have been various hacks around this presented by the DPDK > community, essentially enabling SR-IOV underneath vfio-pci, without the > driver's knowledge. These are very much dis-recommended, IMO. > However, we have added SR-IOV support to the vfio-pci driver in kernel > v5.7 and DPDK support is under development, which represents this trust > and collaboration between PF and VF drivers using a new VF token > concept. I'd encourage you to look for this if your configuration does > require both PF and VF drivers in userspace. A much more normal > configuration to this point has been that the PF makes use of a host > driver (ex. igb, ixgbe, i40e, etc.) while the VF is bound to vfio-pci > for userspace drivers. In this configuration the host driver is > considered trusted and we don't need to invent new mechanisms to > indicate collaboration between userspace drivers. Thanks, > Thanks for the information. Clearly understand what I need to do. Where can I find information on vfio-pci sr-iov support (writeup/design)? Thanks, Ravi > > Alex > >
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