[PATCH] vfio: Stop using iommu_present()

[PATCH] vfio: Stop using iommu_present()

[Robin Murphy]

IOMMU groups have been mandatory for some time now, so a device without
one is necessarily a device without any usable IOMMU, therefore the
iommu_present() check is redundant (or at best unhelpful).

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/vfio/vfio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index a4555014bd1e..7b0a7b85e77e 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -745,11 +745,11 @@ static struct vfio_group *vfio_group_find_or_alloc(struct device *dev)
 
 	iommu_group = iommu_group_get(dev);
 #ifdef CONFIG_VFIO_NOIOMMU
-	if (!iommu_group && noiommu && !iommu_present(dev->bus)) {
+	if (!iommu_group && noiommu) {
 		/*
 		 * With noiommu enabled, create an IOMMU group for devices that
-		 * don't already have one and don't have an iommu_ops on their
-		 * bus.  Taint the kernel because we're about to give a DMA
+		 * don't already have one, implying no IOMMU hardware/driver
+		 * exists.  Taint the kernel because we're about to give a DMA
 		 * capable device to a user without IOMMU protection.
 		 */
 		group = vfio_noiommu_group_alloc(dev, VFIO_NO_IOMMU);
-- 
2.28.0.dirty

Re: [PATCH] vfio: Stop using iommu_present()

[Jason Gunthorpe]

On Tue, Apr 05, 2022 at 01:11:54PM +0100, Robin Murphy wrote:
> IOMMU groups have been mandatory for some time now, so a device without
> one is necessarily a device without any usable IOMMU, therefore the
> iommu_present() check is redundant (or at best unhelpful).
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/vfio/vfio.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason

Re: [PATCH] vfio: Stop using iommu_present()

[Alex Williamson]

On Tue,  5 Apr 2022 13:11:54 +0100
Robin Murphy <robin.murphy@arm.com> wrote:

> IOMMU groups have been mandatory for some time now, so a device without
> one is necessarily a device without any usable IOMMU, therefore the
> iommu_present() check is redundant (or at best unhelpful).
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/vfio/vfio.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index a4555014bd1e..7b0a7b85e77e 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -745,11 +745,11 @@ static struct vfio_group *vfio_group_find_or_alloc(struct device *dev)
>  
>  	iommu_group = iommu_group_get(dev);
>  #ifdef CONFIG_VFIO_NOIOMMU
> -	if (!iommu_group && noiommu && !iommu_present(dev->bus)) {
> +	if (!iommu_group && noiommu) {
>  		/*
>  		 * With noiommu enabled, create an IOMMU group for devices that
> -		 * don't already have one and don't have an iommu_ops on their
> -		 * bus.  Taint the kernel because we're about to give a DMA
> +		 * don't already have one, implying no IOMMU hardware/driver
> +		 * exists.  Taint the kernel because we're about to give a DMA
>  		 * capable device to a user without IOMMU protection.
>  		 */
>  		group = vfio_noiommu_group_alloc(dev, VFIO_NO_IOMMU);

Applied to vfio next branch for v5.19.  Thanks,

Alex