On Wed, Mar 23, 2022 at 05:34:18PM -0300, Jason Gunthorpe wrote: > Stated another way, any platform that wires dev_is_dma_coherent() to > true, like all x86 does, must support IOMMU_CACHE and report > IOMMU_CAP_CACHE_COHERENCY for every iommu_domain the platform > supports. The platform obviously declares it support this in order to > support the in-kernel DMA API. That gives me a nice simple idea: diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c index 3c6b95ad026829..8366884df4a030 100644 --- a/drivers/iommu/iommufd/device.c +++ b/drivers/iommu/iommufd/device.c @@ -8,6 +8,7 @@ #include <linux/pci.h> #include <linux/irqdomain.h> #include <linux/dma-iommu.h> +#include <linux/dma-map-ops.h> #include "iommufd_private.h" @@ -61,6 +62,10 @@ struct iommufd_device *iommufd_bind_pci_device(int fd, struct pci_dev *pdev, struct iommu_group *group; int rc; + /* iommufd always uses IOMMU_CACHE */ + if (!dev_is_dma_coherent(&pdev->dev)) + return ERR_PTR(-EINVAL); + ictx = iommufd_fget(fd); if (!ictx) return ERR_PTR(-EINVAL); diff --git a/drivers/iommu/iommufd/ioas.c b/drivers/iommu/iommufd/ioas.c index 48149988c84bbc..3d6df1ffbf93e6 100644 --- a/drivers/iommu/iommufd/ioas.c +++ b/drivers/iommu/iommufd/ioas.c @@ -129,7 +129,8 @@ static int conv_iommu_prot(u32 map_flags) * We provide no manual cache coherency ioctls to userspace and most * architectures make the CPU ops for cache flushing privileged. * Therefore we require the underlying IOMMU to support CPU coherent - * operation. + * operation. Support for IOMMU_CACHE is enforced by the + * dev_is_dma_coherent() test during bind. */ iommu_prot = IOMMU_CACHE; if (map_flags & IOMMU_IOAS_MAP_WRITEABLE) Looking at it I would say all the places that test IOMMU_CAP_CACHE_COHERENCY can be replaced with dev_is_dma_coherent() except for the one call in VFIO that is supporting the Intel no-snoop behavior. Then we can rename IOMMU_CAP_CACHE_COHERENCY to something like IOMMU_CAP_ENFORCE_CACHE_COHERENCY and just create a IOMMU_ENFORCE_CACHE prot flag for Intel IOMMU to use instead of abusing IOMMU_CACHE. Jason
