On Fri, 24 Jun 2022 18:51:44 +0100 Robin Murphy <robin.murphy@xxxxxxx> wrote: > Since IOMMU groups are mandatory for drivers to support, it stands to > reason that any device which has been successfully added to a group > must be on a bus supported by that IOMMU driver, and therefore a domain > viable for any device in the group must be viable for all devices in > the group. This already has to be the case for the IOMMU API's internal > default domain, for instance. Thus even if the group contains devices on > different buses, that can only mean that the IOMMU driver actually > supports such an odd topology, and so without loss of generality we can > expect the bus type of any device in a group to be suitable for IOMMU > API calls. > > Furthermore, scrutiny reveals a lack of protection for the bus being > removed while vfio_iommu_type1_attach_group() is using it; the reference > that VFIO holds on the iommu_group ensures that data remains valid, but > does not prevent the group's membership changing underfoot. > > We can address both concerns by recycling vfio_bus_type() into some > superficially similar logic to indirect the IOMMU API calls themselves. > Each call is thus protected from races by the IOMMU group's own locking, > and we no longer need to hold group-derived pointers beyond that scope. > It also gives us an easy path for the IOMMU API's migration of bus-based > interfaces to device-based, of which we can already take the first step > with device_iommu_capable(). As with domains, any capability must in > practice be consistent for devices in a given group - and after all it's > still the same capability which was expected to be consistent across an > entire bus! - so there's no need for any complicated validation. > > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx> > --- Applied series to vfio next branch for v5.20. Thanks, Alex > v3: Complete rewrite yet again, and finally it doesn't feel like we're > stretching any abstraction boundaries the wrong way, and the diffstat > looks right too. I did think about embedding IOMMU_CAP_INTR_REMAP > directly in the callback, but decided I like the consistency of minimal > generic wrappers. And yes, if the capability isn't supported then it > does end up getting tested for the whole group, but meh, it's harmless. > > drivers/vfio/vfio_iommu_type1.c | 42 +++++++++++++++++---------------- > 1 file changed, 22 insertions(+), 20 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index c13b9290e357..a77ff00c677b 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -1679,18 +1679,6 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu, > return ret; > } > > -static int vfio_bus_type(struct device *dev, void *data) > -{ > - struct bus_type **bus = data; > - > - if (*bus && *bus != dev->bus) > - return -EINVAL; > - > - *bus = dev->bus; > - > - return 0; > -} > - > static int vfio_iommu_replay(struct vfio_iommu *iommu, > struct vfio_domain *domain) > { > @@ -2153,13 +2141,25 @@ static void vfio_iommu_iova_insert_copy(struct vfio_iommu *iommu, > list_splice_tail(iova_copy, iova); > } > > +static int vfio_iommu_device_capable(struct device *dev, void *data) > +{ > + return device_iommu_capable(dev, (enum iommu_cap)data); > +} > + > +static int vfio_iommu_domain_alloc(struct device *dev, void *data) > +{ > + struct iommu_domain **domain = data; > + > + *domain = iommu_domain_alloc(dev->bus); > + return 1; /* Don't iterate */ > +} > + > static int vfio_iommu_type1_attach_group(void *iommu_data, > struct iommu_group *iommu_group, enum vfio_group_type type) > { > struct vfio_iommu *iommu = iommu_data; > struct vfio_iommu_group *group; > struct vfio_domain *domain, *d; > - struct bus_type *bus = NULL; > bool resv_msi, msi_remap; > phys_addr_t resv_msi_base = 0; > struct iommu_domain_geometry *geo; > @@ -2192,18 +2192,19 @@ static int vfio_iommu_type1_attach_group(void *iommu_data, > goto out_unlock; > } > > - /* Determine bus_type in order to allocate a domain */ > - ret = iommu_group_for_each_dev(iommu_group, &bus, vfio_bus_type); > - if (ret) > - goto out_free_group; > - > ret = -ENOMEM; > domain = kzalloc(sizeof(*domain), GFP_KERNEL); > if (!domain) > goto out_free_group; > > + /* > + * Going via the iommu_group iterator avoids races, and trivially gives > + * us a representative device for the IOMMU API call. We don't actually > + * want to iterate beyond the first device (if any). > + */ > ret = -EIO; > - domain->domain = iommu_domain_alloc(bus); > + iommu_group_for_each_dev(iommu_group, &domain->domain, > + vfio_iommu_domain_alloc); > if (!domain->domain) > goto out_free_domain; > > @@ -2258,7 +2259,8 @@ static int vfio_iommu_type1_attach_group(void *iommu_data, > list_add(&group->next, &domain->group_list); > > msi_remap = irq_domain_check_msi_remap() || > - iommu_capable(bus, IOMMU_CAP_INTR_REMAP); > + iommu_group_for_each_dev(iommu_group, (void *)IOMMU_CAP_INTR_REMAP, > + vfio_iommu_device_capable); > > if (!allow_unsafe_interrupts && !msi_remap) { > pr_warn("%s: No interrupt remapping support. Use the module param \"allow_unsafe_interrupts\" to enable VFIO IOMMU support on this platform\n",