Re: [PATCH v2 1/2] iommu: Prevent RESV_DIRECT devices from blocking domains

[Jason Gunthorpe]

On Thu, Jul 13, 2023 at 12:32:47PM +0800, Lu Baolu wrote:
> The IOMMU_RESV_DIRECT flag indicates that a memory region must be mapped
> 1:1 at all times. This means that the region must always be accessible to
> the device, even if the device is attached to a blocking domain. This is
> equal to saying that IOMMU_RESV_DIRECT flag prevents devices from being
> attached to blocking domains.
> 
> This also implies that devices that implement RESV_DIRECT regions will be
> prevented from being assigned to user space since taking the DMA ownership
> immediately switches to a blocking domain.
> 
> The rule of preventing devices with the IOMMU_RESV_DIRECT regions from
> being assigned to user space has existed in the Intel IOMMU driver for
> a long time. Now, this rule is being lifted up to a general core rule,
> as other architectures like AMD and ARM also have RMRR-like reserved
> regions. This has been discussed in the community mailing list and refer
> to below link for more details.
> 
> Other places using unmanaged domains for kernel DMA must follow the
> iommu_get_resv_regions() and setup IOMMU_RESV_DIRECT - we do not restrict
> them in the core code.
> 
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Link: https://lore.kernel.org/linux-iommu/BN9PR11MB5276E84229B5BD952D78E9598C639@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  include/linux/iommu.h |  2 ++
>  drivers/iommu/iommu.c | 37 +++++++++++++++++++++++++++----------
>  2 files changed, 29 insertions(+), 10 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason