linux-kernel - Re: [PATCH] vfio: Stop using iommu

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Date:   Thu, 12 May 2022 12:21:21 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     cohuck@...hat.com, iommu@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio: Stop using iommu_present()

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