SOC-integrated devices on some platforms require their PCI ATS enabled
for operation when the IOMMU is in scalable mode. Those devices are
reported via ACPI/SATC table with the ATC_REQUIRED bit set in the Flags
field.
The PCI subsystem offers the 'pci=noats' kernel command to disable PCI
ATS on all devices. Using 'pci=noat' with devices that require PCI ATS
can cause a conflict, leading to boot failure, especially if the device
is a graphics device.
To prevent this issue, check PCI ATS support before enumerating the IOMMU
devices. If any device requires PCI ATS, but PCI ATS is disabled by
'pci=noats', switch the IOMMU to operate in legacy mode to ensure
successful booting.
Fixes: 97f2f2c5317f ("iommu/vt-d: Enable ATS for the devices in SATC table")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12036
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
drivers/iommu/intel/iommu.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 4aa070cf56e7..8f275e046e91 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -3127,10 +3127,26 @@ int dmar_iommu_notify_scope_dev(struct dmar_pci_notify_info *info)
(void *)satc + satc->header.length,
satc->segment, satcu->devices,
satcu->devices_cnt);
- if (ret > 0)
- break;
- else if (ret < 0)
+ if (ret < 0)
return ret;
+
+ if (ret > 0) {
+ /*
+ * The device requires PCI/ATS when the IOMMU
+ * works in the scalable mode. If PCI/ATS is
+ * disabled using the pci=noats kernel parameter,
+ * the IOMMU will default to legacy mode. Users
+ * are informed of this change.
+ */
+ if (intel_iommu_sm && satcu->atc_required &&
+ !pci_ats_supported(info->dev)) {
+ pci_warn(info->dev,
+ "PCI/ATS not supported, system working in IOMMU legacy mode\n");
+ intel_iommu_sm = 0;
+ }
+
+ break;
+ }
} else if (info->event == BUS_NOTIFY_REMOVED_DEVICE) {
if (dmar_remove_dev_scope(info, satc->segment,
satcu->devices, satcu->devices_cnt))
--
2.34.1
