FAILED: Patch "iommu/vt-d: Flush dev-IOTLB only when PCIe device is accessible in scalable mode" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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 10e60d87813989e20eac1f3eda30b3bae461e7f9 Mon Sep 17 00:00:00 2001
From: Jinhui Guo <[email protected]>
Date: Thu, 22 Jan 2026 09:48:51 +0800
Subject: [PATCH] iommu/vt-d: Flush dev-IOTLB only when PCIe device is
accessible in scalable mode
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Commit 4fc82cd907ac ("iommu/vt-d: Don't issue ATS Invalidation request when device is disconnected") relies on pci_dev_is_disconnected() to skip ATS invalidation for safely-removed devices, but it does not cover link-down caused by faults, which can still hard-lock the system.

For example, if a VM fails to connect to the PCIe device, "virsh destroy" is executed to release resources and isolate the fault, but a hard-lockup occurs while releasing the group fd.

Call Trace:
 qi_submit_sync
 qi_flush_dev_iotlb
 intel_pasid_tear_down_entry
 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

Although pci_device_is_present() is slower than pci_dev_is_disconnected(), it still takes only ~70 µs on a ConnectX-5 (8 GT/s, x2) and becomes even faster as PCIe speed and width increase.

Besides, devtlb_invalidation_with_pasid() is called only in the paths below, which are far less frequent than memory map/unmap.

1. mm-struct release
2. {attach,release}_dev
3. set/remove PASID
4. dirty-tracking setup

The gain in system stability far outweighs the negligible cost of using pci_device_is_present() instead of pci_dev_is_disconnected() to decide when to skip ATS invalidation, especially under GDR high-load conditions.

---
 drivers/iommu/intel/pasid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 3f6d78180d799..99692f88b8834 100644
@@ -218,7 +218,7 @@ devtlb_invalidation_with_pasid(struct intel_iommu *iommu,
 	if (!info || !info->ats_enabled)
 		return;
 
-	if (pci_dev_is_disconnected(to_pci_dev(dev)))
+	if (!pci_device_is_present(to_pci_dev(dev)))
 		return;
 
 	sid = PCI_DEVID(info->bus, info->devfn);

2.51.0