FAILED: Patch "iommu/vt-d: Skip dev-iotlb flush for inaccessible PCIe device without scalable mode" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 42662d19839f34735b718129ea200e3734b07e50 Mon Sep 17 00:00:00 2001
From: Jinhui Guo <[email protected]>
Date: Thu, 22 Jan 2026 09:48:50 +0800
Subject: [PATCH] iommu/vt-d: Skip dev-iotlb flush for inaccessible PCIe device
without scalable mode
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

PCIe endpoints with ATS enabled and passed through to userspace (e.g., QEMU, DPDK) can hard-lock the host when their link drops, either by surprise removal or by a link fault.

Commit 4fc82cd907ac ("iommu/vt-d: Don't issue ATS Invalidation request when device is disconnected") adds pci_dev_is_disconnected() to devtlb_invalidation_with_pasid() so ATS invalidation is skipped only when the device is being safely removed, but it applies only when Intel IOMMU scalable mode is enabled.

With scalable mode disabled or unsupported, a system hard-lock occurs when a PCIe endpoint's link drops because the Intel IOMMU waits indefinitely for an ATS invalidation that cannot complete.

Call Trace:
 qi_submit_sync
 qi_flush_dev_iotlb
 __context_flush_dev_iotlb.part.0
 domain_context_clear_one_cb
 pci_for_each_dma_alias
 device_block_translation
 blocking_domain_attach_dev
 iommu_deinit_device
 __iommu_group_remove_device
 iommu_release_device
 iommu_bus_notifier
 blocking_notifier_call_chain
 bus_notify
 device_del
 pci_remove_bus_device
 pci_stop_and_remove_bus_device
 pciehp_unconfigure_device
 pciehp_disable_slot
 pciehp_handle_presence_or_link_change
 pciehp_ist

Commit 81e921fd3216 ("iommu/vt-d: Fix NULL domain on device release") adds intel_pasid_teardown_sm_context() to intel_iommu_release_device(), which calls qi_flush_dev_iotlb() and can also hard-lock the system when a PCIe endpoint's link drops.

Call Trace:
 qi_submit_sync
 qi_flush_dev_iotlb
 __context_flush_dev_iotlb.part.0
 intel_context_flush_no_pasid
 device_pasid_table_teardown
 pci_pasid_table_teardown
 pci_for_each_dma_alias
 intel_pasid_teardown_sm_context
 intel_iommu_release_device
 iommu_deinit_device
 __iommu_group_remove_device
 iommu_release_device
 iommu_bus_notifier
 blocking_notifier_call_chain
 bus_notify
 device_del
 pci_remove_bus_device
 pci_stop_and_remove_bus_device
 pciehp_unconfigure_device
 pciehp_disable_slot
 pciehp_handle_presence_or_link_change
 pciehp_ist

Sometimes the endpoint loses connection without a link-down event (e.g., due to a link fault); killing the process (virsh destroy) then hard-locks the host.

Call Trace:
 qi_submit_sync
 qi_flush_dev_iotlb
 __context_flush_dev_iotlb.part.0
 domain_context_clear_one_cb
 pci_for_each_dma_alias
 device_block_translation
 blocking_domain_attach_dev
 __iommu_attach_device
 __iommu_device_set_domain
 __iommu_group_set_domain_internal
 iommu_detach_group
 vfio_iommu_type1_detach_group
 vfio_group_detach_container
 vfio_group_fops_release
 __fput

pci_dev_is_disconnected() only covers safe-removal paths; pci_device_is_present() tests accessibility by reading vendor/device IDs and internally calls pci_dev_is_disconnected(). On a ConnectX-5 (8 GT/s, x2) this costs ~70 µs.

Since __context_flush_dev_iotlb() is only called on {attach,release}_dev paths (not hot), add pci_device_is_present() there to skip inaccessible devices and avoid the hard-lock.

---
 drivers/iommu/intel/pasid.c | 8 ++++++++
 1 file changed, 8 insertions(+)

index 3e2255057079c..3f6d78180d799 100644
@@ -1102,6 +1102,14 @@ static void __context_flush_dev_iotlb(struct device_domain_info *info)
 	if (!info->ats_enabled)
 		return;
 
+	/*
+	 * Skip dev-IOTLB flush for inaccessible PCIe devices to prevent the
+	 * Intel IOMMU from waiting indefinitely for an ATS invalidation that
+	 * cannot complete.
+	 */
+	if (!pci_device_is_present(to_pci_dev(info->dev)))
+		return;
+
 	qi_flush_dev_iotlb(info->iommu, PCI_DEVID(info->bus, info->devfn),
 			   info->pfsid, info->ats_qdep, 0, MAX_AGAW_PFN_WIDTH);
 

2.51.0