Messages in this thread | | | Subject | Re: [PATCH] iommu/amd: Enable swiotlb if any device supports iommu v2 and uses identity mapping | From | Robin Murphy <> | Date | Thu, 8 Jul 2021 11:18:45 +0100 |
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On 2021-07-08 10:28, Joerg Roedel wrote: > On Thu, Jul 08, 2021 at 03:42:32PM +0800, Kai-Heng Feng wrote: >> @@ -344,6 +344,9 @@ static int iommu_init_device(struct device *dev) >> >> iommu = amd_iommu_rlookup_table[dev_data->devid]; >> dev_data->iommu_v2 = iommu->is_iommu_v2; >> + >> + if (dev_data->iommu_v2) >> + swiotlb = 1; > > This looks like the big hammer, as it will affect all other systems > where the AMD GPUs are in their own group. > > What is needed here is an explicit check whether a non-iommu-v2 device > is direct-mapped because it shares a group with the GPU, and only enable > swiotlb in this case.
Right, it's basically about whether any DMA-limited device might at any time end up in an IOMMU_DOMAIN_IDENTITY domain. And given the possibility of device hotplug and the user being silly with the sysfs interface, I don't think we can categorically determine that at boot time.
Also note that Intel systems are likely to be similarly affected (in fact intel-iommu doesn't even have the iommu_default_passthough() check so it's probably even easier to blow up).
Robin.
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