On Tuesday, October 20, 2026 1:55 AM Robin Murphy wrote: > On 16/10/2026 7:46 am, Mikko Perttunen wrote: > > ARM's arch_setup_dma_ops / arm_setup_iommu_dma_ops creates a custom > > IOMMU domain for DMA API usage, and continues to do so when the IOMMU > > driver doesn't explicitly request a DMA default domain type. > > > > When, however, that DMA default domain is requested and the core owns > > the domain, we need to skip our own domain management. Add checks to > > arm_setup/teardown_iommu_dma_ops for these cases. In such a case IOVAs > > can be allocated from anywhere in the domain's geometry, so also add a > > check to ensure the device's dma-ranges cover it. Presently, this is the > > case for all platforms except some OMAP platforms with a non-zero > > dma-ranges base. > > It's probably worth adding some cleverness to arm_iommu_detach_device() > as well - it might work out benign to attempt to detach from a real > core-owned default domain, but we'll now want to set dma_ops and > to_dma_iommu_mapping according to the default domain itself (since we'll > now have the possibility of switching between an explicit unmanaged > dma_iommu_mapping and the implicit default one.)
I was thinking of just disallowing the explicit arm_iommu_* API for devices that get a default domain and hoping that any device that opts in to the "modern way" is capable of getting rid of the custom handling :) I'll add a check to arm_iommu_attach_device to disallow it if there's a core owned domain unless you have other thoughts. Thanks, Mikko > > Thanks, > Robin. > > > Signed-off-by: Mikko Perttunen <[email protected]> > > --- > > arch/arm/mm/dma-mapping.c | 25 ++++++++++++++++++++++++- > > 1 file changed, 24 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c > > index f2d3e8ec3487..d6315baeddb9 100644 > > --- a/arch/arm/mm/dma-mapping.c > > +++ b/arch/arm/mm/dma-mapping.c > > @@ -1761,13 +1761,33 @@ EXPORT_SYMBOL_GPL(arm_iommu_detach_device); > > > > static void arm_setup_iommu_dma_ops(struct device *dev) > > { > > - struct dma_iommu_mapping *mapping; > > + struct dma_iommu_mapping *mapping = to_dma_iommu_mapping(dev); > > u64 dma_base = 0, size = 1ULL << 32; > > > > if (dev->dma_range_map) { > > dma_base = dma_range_map_min(dev->dma_range_map); > > size = dma_range_map_max(dev->dma_range_map) - dma_base; > > } > > + > > + /* > > + * An existing cookie means the core owns the domain. Only set the > > + * per-binding DMA ops. IOVAs are allocated from the whole aperture, > > + * so the device's dma-ranges must cover it. > > + */ > > + if (mapping) { > > + const struct iommu_domain_geometry *geo = > > + &mapping->domain->geometry; > > + > > + if (dma_base > geo->aperture_start || > > + dma_base + size < geo->aperture_end) { > > + dev_err(dev, "dma-ranges do not cover the IOMMU > > aperture\n"); > > + return; > > + } > > + > > + set_dma_ops(dev, &iommu_ops); > > + return; > > + } > > + > > mapping = arm_iommu_create_mapping(dev, dma_base, size); > > if (IS_ERR(mapping)) { > > pr_warn("Failed to create %llu-byte IOMMU mapping for device > > %s\n", > > @@ -1792,6 +1812,9 @@ static void arm_teardown_iommu_dma_ops(struct device > > *dev) > > if (!mapping) > > return; > > > > + if (!mapping->owns_domain) > > + return; > > + > > arm_iommu_detach_device(dev); > > arm_iommu_release_mapping(mapping); > > } > > > >
