PCI: Add pci_ats_required() for CXL.cache capable devices

Controlled by IOMMU drivers, ATS can be enabled "on demand", when a given
PASID on a device is attached to an I/O page table. This is working, even
when a device has no translation on its RID (i.e., RID is IOMMU bypassed).

However, certain PCIe devices require non-PASID ATS on their RID even when
the RID is IOMMU bypassed. Call this "ATS always on" in IOMMU term.

For example, CXL spec r4.0 notes in sec 3.2.5.13 Memory Type on CXL.cache:
 "To source requests on CXL.cache, devices need to get the Host Physical
  Address (HPA) from the Host by means of an ATS request on CXL.io."

In other words, the CXL.cache capability requires ATS; otherwise, it can't
access host physical memory.

Introduce a new pci_ats_required() helper for the IOMMU driver to scan a
PCI device and shift ATS policies between "on demand" and "always on".

Add the support for CXL.cache devices first. Pre-CXL devices will be added
in quirks.c file.

Note that pci_ats_required() validates against pci_ats_supported(), so we
ensure that untrusted devices (e.g. external ports) will not be always on.
This maintains the existing ATS security policy regarding potential side-
channel attacks via ATS.

Cc: linux-cxl@vger.kernel.org
Suggested-by: Vikram Sethi <vsethi@nvidia.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Nirmoy Das <nirmoyd@nvidia.com>
Acked-by: Nirmoy Das <nirmoyd@nvidia.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

0 files changed, 0 insertions, 0 deletions