iommu: Attach device group to old domain in error path

[ Upstream commit 2eb19a266a7351ebc71fd452a97d9c32d8b5c716 ]

iommu_attach_group() attaches all devices in a group to domain and then
sets group domain (group->domain). Current code (__iommu_attach_group())
does not handle error path. This creates problem as devices to domain
attachment is in inconsistent state.

Flow:
  - During boot iommu attach devices to default domain
  - Later some device driver (like amd/iommu_v2 or vfio) tries to attach
    device to new domain.
  - In iommu_attach_group() path we detach device from current domain.
    Then it tries to attach devices to new domain.
  - If it fails to attach device to new domain then device to domain link
    is broken.
  - iommu_attach_group() returns error.
  - At this stage iommu_attach_group() caller thinks, attaching device to
    new domain failed and devices are still attached to old domain.
  - But in reality device to old domain link is broken. It will result
    in all sort of failures (like IO page fault) later.

To recover from this situation, we need to attach all devices back to the
old domain. Also log warning if it fails attach device back to old domain.

Suggested-by: Lu Baolu <baolu.lu@linux.intel.com>
Reported-by: Matt Fagnani <matt.fagnani@bell.net>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Matt Fagnani <matt.fagnani@bell.net>
Link: https://lore.kernel.org/r/20230215052642.6016-1-vasant.hegde@amd.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216865
Link: https://lore.kernel.org/lkml/15d0f9ff-2a56-b3e9-5b45-e6b23300ae3b@leemhuis.info/
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index fd8c8aeb3c504f97f099a42fe2a3c43af3cac643..bfb2f163c6914a9fbb82564328657d04b05a0b69 100644 (file)
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2089,8 +2089,22 @@ static int __iommu_attach_group(struct iommu_domain *domain,
 
        ret = __iommu_group_for_each_dev(group, domain,
                                         iommu_group_do_attach_device);
-       if (ret == 0)
+       if (ret == 0) {
                group->domain = domain;
+       } else {
+               /*
+                * To recover from the case when certain device within the
+                * group fails to attach to the new domain, we need force
+                * attaching all devices back to the old domain. The old
+                * domain is compatible for all devices in the group,
+                * hence the iommu driver should always return success.
+                */
+               struct iommu_domain *old_domain = group->domain;
+
+               group->domain = NULL;
+               WARN(__iommu_group_set_domain(group, old_domain),
+                    "iommu driver failed to attach a compatible domain");
+       }
 
        return ret;
 }