Hi Baolu, On Mon, Jul 24, 2023 at 02:03:51PM +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> > Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Acked-by: Joerg Roedel <jroedel@xxxxxxx> Feel free to include that in your next round of VT-d updates you send my way.
