On Wed, Jul 01, 2026 at 06:45:11AM +1000, Dave Airlie wrote: > > Dave could be facing a fabric issue. AFAIK the ATS invalidation that > > the iommu=strict pushses should fence the fabric so would resolve a > > missing fabric fence. I suppose if you don't see any evidence of a > > non-present ATS response explosion with strict then this would be a > > really good theory. > > It's definitely a fabric issue, the iommu ATS invalidation is what > "fixes" it, but I'm not figuring out how to flush it from the GPU > side, and I'm not seeing where the official driver does this either, > guess I have to keep digging. Maybe Alistair knows something.
Well, as I said the ATS does two things, it fences the fabric and it will fail DMAs with ATS non-present (which doesn't trigger an iommu log). If you are confident there are no ATS non-present events inside the GPU then fabric is the best guess, but most likely the fabric will clear in microseconds after the last GPU DMA so it would be a pretty narrow race. > From the ubuntu kernel this thing ships with: > https://bugs.launchpad.net/ubuntu/+source/linux-nvidia-6.14/+bug/2132033 > > "Add two more Spark iGPU IDs for the existing iommu quirk " > > diff -u linux-nvidia-6.14-6.14.0/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > linux-nvidia-6.14-6.14.0/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > --- linux-nvidia-6.14-6.14.0/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ linux-nvidia-6.14-6.14.0/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -3654,7 +3654,9 @@ > if (IS_HISI_PTT_DEVICE(pdev)) > return IOMMU_DOMAIN_IDENTITY; > > - if (pdev->vendor == PCI_VENDOR_ID_NVIDIA && pdev->device == 0x2E12) > + if (pdev->vendor == PCI_VENDOR_ID_NVIDIA && > + (pdev->device == 0x2E12 || pdev->device == 0x2E2A || > + pdev->device == 0x2E2B)) > return IOMMU_DOMAIN_DMA; > } > > > I should probably work out if anything upstream does this or if I can > mess up the production driver against an upstream kernel. Latest upstream has this fixed now in a different way, this is about forcing ATS mode on inside the SMMU driver because spark can't work if ATS is disabled. Jason
