[ Upstream commit 3247bd10 ]

All Intel platforms guarantee that all root complex implementations must
send transactions up to IOMMU for address translations. Hence for Intel
RCiEP devices, we can assume some ACS-type isolation even without an ACS
capability.

From the Intel VT-d spec, r3.1, sec 3.16 ("Root-Complex Peer to Peer
Considerations"):

  When DMA remapping is enabled, peer-to-peer requests through the
  Root-Complex must be handled as follows:

  - The input address in the request is translated (through first-level,
    second-level or nested translation) to a host physical address (HPA).
    The address decoding for peer addresses must be done only on the
    translated HPA. Hardware implementations are free to further limit
    peer-to-peer accesses to specific host physical address regions (or
    to completely disallow peer-forwarding of translated requests).

  - Since address translation changes the contents (address field) of
    the PCI Express Transaction Layer Packet (TLP), for PCI Express
    peer-to-peer requests with ECRC, the Root-Complex hardware must use
    the new ECRC (re-computed with the translated address) if it
    decides to forward the TLP as a peer request.

  - Root-ports, and multi-function root-complex integrated endpoints, may
    support additional peer-to-peer control features by supporting PCI
    Express Access Control Services (ACS) capability. Refer to ACS
    capability in PCI Express specifications for details.

Since Linux didn't give special treatment to allow this exception, certain
RCiEP MFD devices were grouped in a single IOMMU group. This doesn't permit
a single device to be assigned to a guest for instance.

In one vendor system: Device 14.x were grouped in a single IOMMU group.

  /sys/kernel/iommu_groups/5/devices/0000:00:14.0
  /sys/kernel/iommu_groups/5/devices/0000:00:14.2
  /sys/kernel/iommu_groups/5/devices/0000:00:14.3

After this patch:

  /sys/kernel/iommu_groups/5/devices/0000:00:14.0
  /sys/kernel/iommu_groups/5/devices/0000:00:14.2
  /sys/kernel/iommu_groups/6/devices/0000:00:14.3 <<< new group

14.0 and 14.2 are integrated devices, but legacy end points, whereas 14.3
was a PCIe-compliant RCiEP.

  00:14.3 Network controller: Intel Corporation Device 9df0 (rev 30)
    Capabilities: [40] Express (v2) Root Complex Integrated Endpoint, MSI 00

This permits assigning this device to a guest VM.

[bhelgaas: drop "Fixes" tag since this doesn't fix a bug in that commit]
Link: https://lore.kernel.org/r/1590699462-7131-1-git-send-email-ashok.raj@intel.comTested-by: Darrel Goeddel <dgoeddel@forcepoint.com>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Cc: stable@vger.kernel.org
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Mark Scott <mscott@forcepoint.com>,
Cc: Romil Sharma <rsharma@forcepoint.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>