On Thu, 7 Apr 2022 12:23:31 -0300 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Thu, Apr 07, 2022 at 04:17:11PM +0100, Robin Murphy wrote: > > > For the specific case of overriding PCIe No Snoop (which is more problematic > > from an Arm SMMU PoV) when assigning to a VM, would that not be easier > > solved by just having vfio-pci clear the "Enable No Snoop" control bit in > > the endpoint's PCIe capability? > > Ideally. > > That was rediscussed recently, apparently there are non-compliant > devices and drivers that just ignore the bit. > > Presumably this is why x86 had to move to an IOMMU enforced feature.. I considered this option when implementing the current solution, but ultimately I didn't have confidence in being able to prevent drivers from using device specific means to effect the change anyway. GPUs especially have various back channels to config space. Thanks, Alex
