Re: [PATCH v7 00/10] KVM PCIe/MSI passthrough on ARM/ARM64: kernel part 1/3: iommu changes

[Eric Auger]

Hi Alex, Robin,
On 04/19/2016 06:56 PM, Eric Auger wrote:
> This series introduces the dma-reserved-iommu api used to:
> 
> - create/destroy an iova domain dedicated to reserved iova bindings
> - map/unmap physical addresses onto reserved IOVAs.
> - search for an existing reserved iova mapping matching a PA window
> - determine whether an msi needs to be iommu mapped
> - translate an msi_msg PA address into its IOVA counterpart

Following Robin's review, I understand one important point we have to
clarify is how much this API has to be generic.

I agree with Robin on the fact there is quite a lot of duplication
between this dma-reserved-iommu implementation and dma-iommu
implementation. Maybe we could consider an msi-mapping API
implementation upon dma-iommu.c. This implementation would add MSI
doorbell binding list management, including, ref counting and locking.

We would need to add a map/unmap function taking an iova/pa/size as
parameters in current dma-iommu.c

An important assumption is that the dma-mapping API and the msi-mapping
API must not be used concurrently (be would be trying to use the same
cookie to store a different iova_domain).

Any thought/suggestion?

Best Regards

Eric


> 
> Currently reserved IOVAs are meant to map MSI physical doorbells. A single
> reserved domain does exit per domain.
> 
> Also a new domain attribute is introduced to signal whether the MSI
> addresses must be mapped in the IOMMU.
> 
> In current usage:
> VFIO subsystem is supposed to create/destroy the iommu reserved domain.
> The MSI layer is supposed to allocate/free iova mappings
> 
> Since several drivers are likely to use the same doorbell, a reference
> counting takes place on the bindings. An RB-tree indexed by PA is used
> to easily lookup for existing mappings at MSI message composition time.
> 
> More details & context can be found at:
> http://www.linaro.org/blog/core-dump/kvm-pciemsi-passthrough-armarm64/
> 
> Best Regards
> 
> Eric
> 
> Git: complete series available at
> https://git.linaro.org/people/eric.auger/linux.git/shortlog/refs/heads/v4.6-rc4-pcie-passthrough-v7
> 
> History:
> 
> v6 -> v7:
> - fixed known lock bugs and multiple page sized slots matching
>   (I currently only have a single MSI frame made of a single page)
> - reserved_iova_cookie now pointing to a struct that encapsulates the
>   iova domain handle + protection attribute passed from VFIO (Alex' req)
> - 2 new functions exposed: iommu_msi_mapping_translate_msg,
>   iommu_msi_mapping_desc_to_domain: not sure this is the right location/proto
>   though
> - iommu_put_reserved_iova now takes a phys_addr_t
> - everything now is cleanup on iommu_domain destruction
> 
> RFC v5 -> patch v6:
> - split to ease the review process
> - in dma-reserved-api use a spin lock instead of a mutex (reported by
>   Jean-Philippe)
> - revisit iommu_get_reserved_iova API to pass a size parameter upon
>   Marc's request
> - Consistently use the page order passed when creating the iova domain.
> - init reserved_binding_list (reported by Julien)
> 
> RFC v4 -> RFC v5:
> - take into account Thomas' comments on MSI related patches
>   - split "msi: IOMMU map the doorbell address when needed"
>   - increase readability and add comments
>   - fix style issues
>  - split "iommu: Add DOMAIN_ATTR_MSI_MAPPING attribute"
>  - platform ITS now advertises IOMMU_CAP_INTR_REMAP
>  - fix compilation issue with CONFIG_IOMMU API unset
>  - arm-smmu-v3 now advertises DOMAIN_ATTR_MSI_MAPPING
> 
> RFC v3 -> v4:
> - Move doorbell mapping/unmapping in msi.c
> - fix ref count issue on set_affinity: in case of a change in the address
>   the previous address is decremented
> - doorbell map/unmap now is done on msi composition. Should allow the use
>   case for platform MSI controllers
> - create dma-reserved-iommu.h/c exposing/implementing a new API dedicated
>   to reserved IOVA management (looking like dma-iommu glue)
> - series reordering to ease the review:
>   - first part is related to IOMMU
>   - second related to MSI sub-system
>   - third related to VFIO (except arm-smmu IOMMU_CAP_INTR_REMAP removal)
> - expose the number of requested IOVA pages through VFIO_IOMMU_GET_INFO
>   [this partially addresses Marc's comments on iommu_get/put_single_reserved
>    size/alignment problematic - which I did not ignore - but I don't know
>    how much I can do at the moment]
> 
> RFC v2 -> RFC v3:
> - should fix wrong handling of some CONFIG combinations:
>   CONFIG_IOVA, CONFIG_IOMMU_API, CONFIG_PCI_MSI_IRQ_DOMAIN
> - fix MSI_FLAG_IRQ_REMAPPING setting in GICv3 ITS (although not tested)
> 
> PATCH v1 -> RFC v2:
> - reverted to RFC since it looks more reasonable ;-) the code is split
>   between VFIO, IOMMU, MSI controller and I am not sure I did the right
>   choices. Also API need to be further discussed.
> - iova API usage in arm-smmu.c.
> - MSI controller natively programs the MSI addr with either the PA or IOVA.
>   This is not done anymore in vfio-pci driver as suggested by Alex.
> - check irq remapping capability of the group
> 
> RFC v1 [2] -> PATCH v1:
> - use the existing dma map/unmap ioctl interface with a flag to register a
>   reserved IOVA range. Use the legacy Rb to store this special vfio_dma.
> - a single reserved IOVA contiguous region now is allowed
> - use of an RB tree indexed by PA to store allocated reserved slots
> - use of a vfio_domain iova_domain to manage iova allocation within the
>   window provided by the userspace
> - vfio alloc_map/unmap_free take a vfio_group handle
> - vfio_group handle is cached in vfio_pci_device
> - add ref counting to bindings
> - user modality enabled at the end of the series
> 
> 
> Eric Auger (10):
>   iommu: Add DOMAIN_ATTR_MSI_MAPPING attribute
>   iommu/arm-smmu: advertise DOMAIN_ATTR_MSI_MAPPING attribute
>   iommu: introduce a reserved iova cookie
>   iommu/dma-reserved-iommu: alloc/free_reserved_iova_domain
>   iommu/dma-reserved-iommu: reserved binding rb-tree and helpers
>   iommu/dma-reserved-iommu: iommu_get/put_reserved_iova
>   iommu/dma-reserved-iommu: delete bindings in
>     iommu_free_reserved_iova_domain
>   iommu/dma-reserved_iommu: iommu_msi_mapping_desc_to_domain
>   iommu/dma-reserved-iommu: iommu_msi_mapping_translate_msg
>   iommu/arm-smmu: call iommu_free_reserved_iova_domain on domain
>     destruction
> 
>  drivers/iommu/Kconfig              |   8 +
>  drivers/iommu/Makefile             |   1 +
>  drivers/iommu/arm-smmu-v3.c        |   4 +
>  drivers/iommu/arm-smmu.c           |   4 +
>  drivers/iommu/dma-reserved-iommu.c | 422 +++++++++++++++++++++++++++++++++++++
>  drivers/iommu/iommu.c              |   2 +
>  include/linux/dma-reserved-iommu.h | 142 +++++++++++++
>  include/linux/iommu.h              |   7 +
>  8 files changed, 590 insertions(+)
>  create mode 100644 drivers/iommu/dma-reserved-iommu.c
>  create mode 100644 include/linux/dma-reserved-iommu.h
>