linux-kernel - [RFC PATCH v9 4/5] iommu/vt-d: don't issue ATS Invalidation request when device is disconnected

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Date: Wed, 27 Dec 2023 19:16:45 -0500
From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
To: bhelgaas@...gle.com,
	baolu.lu@...ux.intel.com,
	dwmw2@...radead.org,
	will@...nel.org,
	robin.murphy@....com,
	lukas@...ner.de
Cc: linux-pci@...r.kernel.org,
	iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v9 4/5] iommu/vt-d: don't issue ATS Invalidation request when device is disconnected

Except those aggressive hotplug cases - surprise remove a hotplug device
while its safe removal is requested and handled in process by:

1. pull it out directly.
2. turn off its power.
3. bring the link down.
4. just died there that moment.

etc, in a word, 'gone' or 'disconnected'.

Mostly are regular normal safe removal and surprise removal unplug.
these hot unplug handling process could be optimized for fix the ATS
Invalidation hang issue by calling pci_dev_is_disconnected() in function
devtlb_invalidation_with_pasid() to check target device state to avoid
sending meaningless ATS Invalidation request to iommu when device is gone.
(see IMPLEMENTATION NOTE in PCIe spec r6.1 section 10.3.1)

For safe removal, device wouldn't be removed untill the whole software
handling process is done, it wouldn't trigger the hard lock up issue
caused by too long ATS Invalidation timeout wait. In safe removal path,
device state isn't set to pci_channel_io_perm_failure in
pciehp_unconfigure_device() by checking 'presence' parameter, calling
pci_dev_is_disconnected() in devtlb_invalidation_with_pasid() will return
false there, wouldn't break the function.

For surprise removal, device state is set to pci_channel_io_perm_failure in
pciehp_unconfigure_device(), means device is already gone (disconnected)
call pci_dev_is_disconnected() in devtlb_invalidation_with_pasid() will
return true to break the function not to send ATS Invalidation request to
the disconnected device blindly, thus avoid the further long time waiting
triggers the hard lockup.

safe removal & surprise removal

pciehp_ist()
   pciehp_handle_presence_or_link_change()
     pciehp_disable_slot()
       remove_board()
         pciehp_unconfigure_device(presence)

Tested-by: Haorong Ye <yehaorong@...edance.com>
Signed-off-by: Ethan Zhao <haifeng.zhao@...ux.intel.com>
---
 drivers/iommu/intel/pasid.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index 1c87fb1b1039..a08bdbec90eb 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -481,6 +481,9 @@ devtlb_invalidation_with_pasid(struct intel_iommu *iommu,
 	if (!info || !info->ats_enabled)
 		return;

+	if (pci_dev_is_disconnected(to_pci_dev(dev)))
+		return;
+
 	sid = info->bus << 8 | info->devfn;
 	qdep = info->ats_qdep;
 	pfsid = info->pfsid;
-- 
2.31.1