On Tue, Jul 14, 2020 at 10:12:49AM +0000, Liu, Yi L wrote: > > Have you verified that this doesn't break the existing usage of > > DOMAIN_ATTR_NESTING in drivers/vfio/vfio_iommu_type1.c? > > I didn't have ARM machine on my hand. But I contacted with Jean > Philippe, he confirmed no compiling issue. I didn't see any code > getting DOMAIN_ATTR_NESTING attr in current drivers/vfio/vfio_iommu_type1.c. > What I'm adding is to call iommu_domai_get_attr(, DOMAIN_ATTR_NESTIN) > and won't fail if the iommu_domai_get_attr() returns 0. This patch > returns an empty nesting info for DOMAIN_ATTR_NESTIN and return > value is 0 if no error. So I guess it won't fail nesting for ARM. I confirm that this series doesn't break the current support for VFIO_IOMMU_TYPE1_NESTING with an SMMUv3. That said... If the SMMU does not support stage-2 then there is a change in behavior (untested): after the domain is silently switched to stage-1 by the SMMU driver, VFIO will now query nesting info and obtain -ENODEV. Instead of succeding as before, the VFIO ioctl will now fail. I believe that's a fix rather than a regression, it should have been like this since the beginning. No known userspace has been using VFIO_IOMMU_TYPE1_NESTING so far, so I don't think it should be a concern. And if userspace queries the nesting properties using the new ABI introduced in this patchset, it will obtain an empty struct. I think that's acceptable, but it may be better to avoid adding the nesting cap if @format is 0? Thanks, Jean > > @Eric, how about your opinion? your dual-stage vSMMU support may > also share the vfio_iommu_type1.c code. > > Regards, > Yi Liu > > > Will
