iommu/vt-d: PRS isn't usable if PDS isn't supported

The specification, Section 7.10, "Software Steps to Drain Page Requests &
Responses," requires software to submit an Invalidation Wait Descriptor
(inv_wait_dsc) with the Page-request Drain (PD=1) flag set, along with
the Invalidation Wait Completion Status Write flag (SW=1). It then waits
for the Invalidation Wait Descriptor's completion.

However, the PD field in the Invalidation Wait Descriptor is optional, as
stated in Section 6.5.2.9, "Invalidation Wait Descriptor":

"Page-request Drain (PD): Remapping hardware implementations reporting
 Page-request draining as not supported (PDS = 0 in ECAP_REG) treat this
 field as reserved."

This implies that if the IOMMU doesn't support the PDS capability, software
can't drain page requests and group responses as expected.

Do not enable PCI/PRI if the IOMMU doesn't support PDS.

Reported-by: Joel Granados <joel.granados@kernel.org>
Closes: https://lore.kernel.org/r/20250909-jag-pds-v1-1-ad8cba0e494e@kernel.org
Fixes: 66ac4db36f4c ("iommu/vt-d: Add page request draining support")
Cc: stable@vger.kernel.org
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20250915062946.120196-1-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 9c3ab9d9f69a3e9e851a411b1f390372172ab700..92759a8f8330e24ac6152bfec2154c93581c8066 100644 (file)
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -3812,7 +3812,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
                        }
 
                        if (info->ats_supported && ecap_prs(iommu->ecap) &&
-                           pci_pri_supported(pdev))
+                           ecap_pds(iommu->ecap) && pci_pri_supported(pdev))
                                info->pri_supported = 1;
                }
        }