db08e1d530
On POWERNV platform, in order to do DMA via IOMMU (i.e. 32bit DMA in our case), a device needs an iommu_table pointer set via set_iommu_table_base(). The codeflow is: - pnv_pci_ioda2_setup_dma_pe() - pnv_pci_ioda2_setup_default_config() - pnv_ioda_setup_bus_dma() [1] pnv_pci_ioda2_setup_dma_pe() creates IOMMU groups, pnv_pci_ioda2_setup_default_config() does default DMA setup, pnv_ioda_setup_bus_dma() takes a bus PE (on IODA2, all physical function PEs as bus PEs except NPU), walks through all underlying buses and devices, adds all devices to an IOMMU group and sets iommu_table. On IODA2, when VFIO is used, it takes ownership over a PE which means it removes all tables and creates new ones (with a possibility of sharing them among PEs). So when the ownership is returned from VFIO to the kernel, the iommu_table pointer written to a device at [1] is stale and needs an update. This adds an "add_to_group" parameter to pnv_ioda_setup_bus_dma() (in fact re-adds as it used to be there a while ago for different reasons) to tell the helper if a device needs to be added to an IOMMU group with an iommu_table update or just the latter. This calls pnv_ioda_setup_bus_dma(..., false) from pnv_ioda2_release_ownership() so when the ownership is restored, 32bit DMA can work again for a device. This does the same thing on obtaining ownership as the iommu_table point is stale at this point anyway and it is safer to have NULL there. We did not hit this earlier as all tested devices in recent years were only using 64bit DMA; the rare exception for this is MPT3 SAS adapter which uses both 32bit and 64bit DMA access and it has not been tested with VFIO much. Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Acked-by: Gavin Shan <gwshan@linux.vnet.ibm.com> Reviewed-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.