On Sun, 29 Jan 2017 23:03:38 +0100 Javier Celaya <[email protected]> wrote:
> The host kernel is version 4.9.0 from Debian Sid. That command outputs > "f0105a". What does it mean? Bit 7 would indicate if the IOMMU supports Snoop Control. When it does, the IOMMU page tables can set the SNP bit, which allows transactions to snoop the processor cache regardless of transaction attributes such as NoSnoop. IOW, it basically negates NoSnoop at the IOMMU level. Since this bit is clear on your IOMMU, we need to register non-coherent DMA with KVM. This affects memory attributes in a few places and determines whether or not KVM needs to emulate the WBINVD (write-back-invalidate) instruction. To some extent, we do need to trust guest memory attributes to work in this mode, however the NoSnoop patch, which simply tries to prevent the device from enabling NoSnoop transactions was a pretty horrible hack. I'm sure that lots of us run with the same IOMMU capabilities, I have a system with identical flags that runs without issue with either an NVIDIA or AMD card. I wonder if the problem is more to do with the fact that your CPU has integrated graphics and you're trying to use x-vga=on without any mention whether you've patched i915 to properly work with VGA arbitration. If the cards support UEFI, you should not need x-vga=on. Is the host primary graphics Intel? I don't understand why the NoSnoop patch would change your results at all. Thanks, Alex _______________________________________________ vfio-users mailing list [email protected] https://www.redhat.com/mailman/listinfo/vfio-users
