linux-kernel - [PATCH v5 3/5] vfio/iommu_type1: Remove the domain->ops comparison

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Date:   Fri, 1 Jul 2022 14:44:53 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     <joro@...tes.org>, <will@...nel.org>, <marcan@...can.st>,
        <sven@...npeter.dev>, <robin.murphy@....com>,
        <robdclark@...il.com>, <baolu.lu@...ux.intel.com>,
        <orsonzhai@...il.com>, <baolin.wang7@...il.com>,
        <zhang.lyra@...il.com>, <jean-philippe@...aro.org>,
        <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>
CC:     <suravee.suthikulpanit@....com>, <alyssa@...enzweig.io>,
        <dwmw2@...radead.org>, <mjrosato@...ux.ibm.com>,
        <gerald.schaefer@...ux.ibm.com>, <thierry.reding@...il.com>,
        <vdumpa@...dia.com>, <jonathanh@...dia.com>, <cohuck@...hat.com>,
        <thunder.leizhen@...wei.com>, <christophe.jaillet@...adoo.fr>,
        <chenxiang66@...ilicon.com>, <john.garry@...wei.com>,
        <yangyingliang@...wei.com>, <iommu@...ts.linux-foundation.org>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-s390@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>, <kvm@...r.kernel.org>
Subject: [PATCH v5 3/5] vfio/iommu_type1: Remove the domain->ops comparison

The domain->ops validation was added, as a precaution, for mixed-driver
systems.

Per Robin's remarks,
* While bus_set_iommu() still exists, the core code prevents multiple
  drivers from registering, so we can't really run into a situation of
  having a mixed-driver system:
  https://lore.kernel.org/kvm/6e1280c5-4b22-ebb3-3912-6c72bc169982@arm.com/

* And there's plenty more significant problems than this to fix; in future
  when many can be permitted, we will rely on the IOMMU core code to check
  the domain->ops:
  https://lore.kernel.org/kvm/6575de6d-94ba-c427-5b1e-967750ddff23@arm.com/

So remove the check in VFIO for simplicity.

Reviewed-by: Kevin Tian <kevin.tian@...el.com>
Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/vfio/vfio_iommu_type1.c | 32 +++++++++++---------------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 7530f0d727e5..5992ee2345a0 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2280,29 +2280,19 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 			domain->domain->ops->enforce_cache_coherency(
 				domain->domain);
 
-	/*
-	 * Try to match an existing compatible domain.  We don't want to
-	 * preclude an IOMMU driver supporting multiple bus_types and being
-	 * able to include different bus_types in the same IOMMU domain, so
-	 * we test whether the domains use the same iommu_ops rather than
-	 * testing if they're on the same bus_type.
-	 */
+	/* Try to match an existing compatible domain */
 	list_for_each_entry(d, &iommu->domain_list, next) {
-		if (d->domain->ops == domain->domain->ops) {
-			iommu_detach_group(domain->domain, group->iommu_group);
-			if (!iommu_attach_group(d->domain,
-						group->iommu_group)) {
-				list_add(&group->next, &d->group_list);
-				iommu_domain_free(domain->domain);
-				kfree(domain);
-				goto done;
-			}
-
-			ret = iommu_attach_group(domain->domain,
-						 group->iommu_group);
-			if (ret)
-				goto out_domain;
+		iommu_detach_group(domain->domain, group->iommu_group);
+		if (!iommu_attach_group(d->domain, group->iommu_group)) {
+			list_add(&group->next, &d->group_list);
+			iommu_domain_free(domain->domain);
+			kfree(domain);
+			goto done;
 		}
+
+		ret = iommu_attach_group(domain->domain,  group->iommu_group);
+		if (ret)
+			goto out_domain;
 	}
 
 	vfio_test_domain_fgsp(domain);
-- 
2.17.1