From: Lu Baolu Date: Thu, 18 Sep 2025 05:02:02 +0000 (+0800) Subject: iommu/vt-d: PRS isn't usable if PDS isn't supported X-Git-Tag: v6.18-rc1~105^2^5~3 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=5ef7e24c742038a5d8c626fdc0e3a21834358341;p=thirdparty%2Flinux.git 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 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 Link: https://lore.kernel.org/r/20250915062946.120196-1-baolu.lu@linux.intel.com Signed-off-by: Joerg Roedel --- diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..92759a8f8330 100644 --- 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; } }