Robin Murphy
2022-Jul-01 10:21 UTC
[PATCH v4 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group
On 2022-06-30 21:36, Nicolin Chen wrote:> Cases like VFIO wish to attach a device to an existing domain that was > not allocated specifically from the device. This raises a condition > where the IOMMU driver can fail the domain attach because the domain and > device are incompatible with each other. > > This is a soft failure that can be resolved by using a different domain. > > Provide a dedicated errno from the IOMMU driver during attach that the > reason attached failed is because of domain incompatability. EMEDIUMTYPE > is chosen because it is never used within the iommu subsystem today and > evokes a sense that the 'medium' aka the domain is incompatible. > > VFIO can use this to know attach is a soft failure and it should continue > searching. Otherwise the attach will be a hard failure and VFIO will > return the code to userspace. > > Update all drivers to return EMEDIUMTYPE in their failure paths that are > related to domain incompatability. Also remove adjacent error prints for > these soft failures, to prevent a kernel log spam, since -EMEDIUMTYPE is > clear enough to indicate an incompatability error. > > Add kdocs describing this behavior. > > Suggested-by: Jason Gunthorpe <jgg at nvidia.com> > Reviewed-by: Kevin Tian <kevin.tian at intel.com> > Signed-off-by: Nicolin Chen <nicolinc at nvidia.com> > ---[...]> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c > index 2ed3594f384e..072cac5ab5a4 100644 > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c > @@ -1135,10 +1135,8 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev) > struct arm_smmu_device *smmu; > int ret; > > - if (!fwspec || fwspec->ops != &arm_smmu_ops) { > - dev_err(dev, "cannot attach to SMMU, is it on the same bus?\n"); > - return -ENXIO; > - } > + if (!fwspec || fwspec->ops != &arm_smmu_ops) > + return -EMEDIUMTYPE;This is the wrong check, you want the "if (smmu_domain->smmu != smmu)" condition further down. If this one fails it's effectively because the device doesn't have an IOMMU at all, and similar to patch #3 it will be removed once the core code takes over properly (I even have both those patches written now!) Thanks, Robin.> /* > * FIXME: The arch/arm DMA API code tries to attach devices to its own