linux-kernel - [PATCH 1/1] iommu/vt-d: Disable PCI ATS in legacy passthrough mode

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Date:   Tue, 14 Nov 2023 09:10:35 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>
Cc:     iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 1/1] iommu/vt-d: Disable PCI ATS in legacy passthrough mode

When IOMMU hardware operates in legacy mode, the TT field of the context
entry determines the translation type, with three supported types (Section
9.3 Context Entry):

- DMA translation without device TLB support
- DMA translation with device TLB support
- Passthrough mode with translated and translation requests blocked

Device TLB support is absent when hardware is configured in passthrough
mode.

Disable the PCI ATS feature when IOMMU is configured for passthrough
translation type in legacy (non-scalable) mode.

Fixes: 0faa19a1515f ("iommu/vt-d: Decouple PASID & PRI enabling from SVA")
Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/intel/iommu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 11670cd812a3..c3ec09118ab1 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1413,6 +1413,10 @@ static void iommu_enable_pci_caps(struct device_domain_info *info)
 	if (!dev_is_pci(info->dev))
 		return;
 
+	if (!sm_supported(info->iommu) && info->domain &&
+	    domain_type_is_si(info->domain))
+		return;
+
 	pdev = to_pci_dev(info->dev);
 
 	/* The PCIe spec, in its wisdom, declares that the behaviour of
-- 
2.34.1