[RFC 0/2] VFIO: Add virtual MSI doorbell support.

Pranavkumar Sawargaonkar
2015-07-24T09:03:28Z

In current VFIO MSI/MSI-X implementation, linux host kernel
allocates MSI/MSI-X vectors when userspace requests through vfio ioctls.
Vfio creates irqfd mappings to notify MSI/MSI-X interrupts
to the userspace when raised.
Guest OS will see emulated MSI/MSI-X controller and receives an interrupt
when kernel notifies the same via irqfd.

Host kernel allocates MSI/MSI-X using standard linux routines
like pci_enable_msix_range() and pci_enable_msi_range().
These routines along with requset_irq() in host kernel sets up
MSI/MSI-X vectors with Physical MSI/MSI-X addresses provided by
interrupt controller driver in host kernel.

This means when a device is assigned with the guest OS, MSI/MSI-X addresses
present in PCIe EP are the PAs programmed by the host linux kernel.

In x86 MSI/MSI-X physical address range is reserved and iommu is aware
about these addreses and transalation is bypassed for these address range.

Unlike x86, ARM/ARM64 does not reserve MSI/MSI-X Physical address range and
all the transactions including MSI go through iommu/smmu without bypass.
This requires extending current vfio MSI layer with additional functionality
for ARM/ARM64 by
1. Programing IOVA (referred as a MSI virtual doorbell address)
in device's MSI vector as a MSI address.
This IOVA will be provided by the userspace based on the
MSI/MSI-X addresses reserved for the guest.
2. Create an IOMMU mapping between this IOVA and
Physical address (PA) assigned to the MSI vector.

This RFC is proposing a solution for MSI/MSI-X passthrough for ARM/ARM64.

Pranavkumar Sawargaonkar (2):
drivers: vfio: iommu map and unmap device specific memory from
kernel.
drivers: vfio: pci: Add virtual MSI doorbell support.

drivers/vfio/pci/vfio_pci.c | 32 ++++++++++++++++++
drivers/vfio/pci/vfio_pci_intrs.c | 64 +++++++++++++++++++++++++++++++++++
drivers/vfio/pci/vfio_pci_private.h | 3 ++
drivers/vfio/vfio.c | 29 ++++++++++++++++
drivers/vfio/vfio_iommu_type1.c | 60 ++++++++++++++++++++++++++++++++
include/linux/vfio.h | 11 +++++-
include/uapi/linux/vfio.h | 19 +++++++++++
7 files changed, 217 insertions(+), 1 deletion(-)

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1.7.9.5