Patch "iommu: Attach device group to old domain in error path" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    iommu: Attach device group to old domain in error path

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     iommu-attach-device-group-to-old-domain-in-error-pat.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c2914e324f4a06a5b27074485d0b92df9601a9ea
Author: Vasant Hegde <vasant.hegde@xxxxxxx>
Date:   Wed Feb 15 05:26:40 2023 +0000

    iommu: Attach device group to old domain in error path
    
    [ Upstream commit 2cc73c5712f97de98c38c2fafc1f288354a9f3c3 ]
    
    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@xxxxxxxxxxxxxxx>
    Reported-by: Matt Fagnani <matt.fagnani@xxxxxxxx>
    Signed-off-by: Vasant Hegde <vasant.hegde@xxxxxxx>
    Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
    Tested-by: Matt Fagnani <matt.fagnani@xxxxxxxx>
    Link: https://lore.kernel.org/r/20230215052642.6016-1-vasant.hegde@xxxxxxx
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=216865
    Link: https://lore.kernel.org/lkml/15d0f9ff-2a56-b3e9-5b45-e6b23300ae3b@xxxxxxxxxxxxx/
    Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index fd8c8aeb3c504..bfb2f163c6914 100644
--- 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;
 }