linux-kernel - [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu

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Date:   Thu, 20 Jul 2017 10:02:33 +0530
From:   Anup Patel <anup.patel@...adcom.com>
To:     Will Deacon <will.deacon@....com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     Scott Branden <sbranden@...adcom.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        Anup Patel <anup.patel@...adcom.com>
Subject: [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu_present()

Not allowing No-IOMMU mode for devices already having
iommu_ops on their bus is very conservative.

We now have IOMMU (such as ARM SMMU) which can bypass
transcations when IOMMU is not configured for a given
device. In addition, it is not necessary to have all
devices on bus to be upstream to an IOMMU on that bus.

Due above reasons, having iommu_present() check for
VFIO No-IOMMU mode is not appropriate.

Signed-off-by: Anup Patel <anup.patel@...adcom.com>
---
 drivers/vfio/vfio.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 330d505..9d90de7 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -124,11 +124,10 @@ struct iommu_group *vfio_iommu_group_get(struct device *dev)
 #ifdef CONFIG_VFIO_NOIOMMU
 	/*
 	 * With noiommu enabled, an IOMMU group will be created for a device
-	 * that doesn't already have one and doesn't have an iommu_ops on their
-	 * bus.  We set iommudata simply to be able to identify these groups
-	 * as special use and for reclamation later.
+	 * that doesn't already have one.  We set iommudata simply to be able
+	 * to identify these groups as special use and for reclamation later.
 	 */
-	if (group || !noiommu || iommu_present(dev->bus))
+	if (group || !noiommu)
 		return group;
 
 	group = iommu_group_alloc();
-- 
2.7.4