Hi Jean, On 7/16/20 5:39 PM, Jean-Philippe Brucker wrote: > 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. But as Yi mentioned ealier, in the current vfio code there is no DOMAIN_ATTR_NESTING query yet. In my SMMUV3 nested stage series, I added such a query in vfio-pci.c to detect if I need to expose a fault region but I already test both the returned value and the output arg. So to me there is no issue with that change. > > 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? agreed Thanks Eric > > 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 >
