Re: [PATCH 0/6] IOMMU/DMA map_resource support for peer-to-peer

[Bjorn Helgaas <bhelgaas@google.com>]

[+cc Yijing, Dave J, Dave M, Alex]

On Fri, May 01, 2015 at 01:32:12PM -0500, wdavis@nvidia.com wrote:
> From: Will Davis <wdavis@nvidia.com>
> 
> Hi,
> 
> This patch series adds DMA APIs to map and unmap a struct resource to and from
> a PCI device's IOVA domain, and implements the AMD, Intel, and nommu versions
> of these interfaces.
> 
> This solves a long-standing problem with the existing DMA-remapping interfaces,
> which require that a struct page be given for the region to be mapped into a
> device's IOVA domain. This requirement cannot support peer device BAR ranges,
> for which no struct pages exist.
> 
> The underlying implementations of map_page and map_sg convert the struct page
> into its physical address anyway, so we just need a way to route the physical
> address of the BAR region to these implementations. The new interfaces do this
> by taking the struct resource describing a device's BAR region, from which the
> physical address is derived.
> 
> The Intel and nommu versions have been verified on a dual Intel Xeon E5405
> workstation. I'm in the process of obtaining hardware to test the AMD version
> as well. Please review.

I think we currently assume there's no peer-to-peer traffic.

I don't know whether changing that will break anything, but I'm concerned
about these:

  - PCIe MPS configuration (see pcie_bus_configure_settings()).

  - PCIe ACS, e.g., pci_acs_enabled().  My guess is that this one is OK,
    but Alex would know better.

  - dma_addr_t.  Currently dma_addr_t is big enough to hold any address
    returned from the DMA API.  That's not necessarily big enough to hold a
    PCI bus address, e.g., a raw BAR value.

> Will Davis (6):
>   dma-debug: add checking for map/unmap_resource
>   DMA-API: Introduce dma_(un)map_resource
>   dma-mapping: pci: add pci_(un)map_resource
>   iommu/amd: Implement (un)map_resource
>   iommu/vt-d: implement (un)map_resource
>   x86: add pci-nommu implementation of map_resource
> 
>  arch/x86/kernel/pci-nommu.c              | 17 +++++++
>  drivers/iommu/amd_iommu.c                | 76 ++++++++++++++++++++++++++------
>  drivers/iommu/intel-iommu.c              | 18 ++++++++
>  include/asm-generic/dma-mapping-broken.h |  9 ++++
>  include/asm-generic/dma-mapping-common.h | 34 ++++++++++++++
>  include/asm-generic/pci-dma-compat.h     | 14 ++++++
>  include/linux/dma-debug.h                | 20 +++++++++
>  include/linux/dma-mapping.h              |  7 +++
>  lib/dma-debug.c                          | 48 ++++++++++++++++++++
>  9 files changed, 230 insertions(+), 13 deletions(-)
> 
> -- 
> 2.3.7
> 
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