[PATCH 2/7] iommu/vt-d: Flush dev-IOTLB only when PCIe device is accessible in scalable mode

[Lu Baolu <baolu.lu@linux.intel.com>]

From: Jinhui Guo <guojinhui.liam@bytedance.com>

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.

Fixes: 4fc82cd907ac ("iommu/vt-d: Don't issue ATS Invalidation request when device is disconnected")
Cc: stable@vger.kernel.org
Signed-off-by: Jinhui Guo <guojinhui.liam@bytedance.com>
Link: https://lore.kernel.org/r/20251211035946.2071-3-guojinhui.liam@bytedance.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/pasid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index 3f6d78180d79..99692f88b883 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -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);
-- 
2.43.0