From: Mario Limonciello mario.limonciello@amd.com
[ Upstream commit 51c33f333bbf7bdb6aa2a327e3a3e4bbb2591511 ]
A BIOS upgrade has changed the IVRS DTE UID for a device that no longer matches the UID in the SSDT. In this case there is only one ACPI device on the system with that _HID but the _UID mismatch.
IVRS: ``` Subtable Type : F0 [Device Entry: ACPI HID Named Device] Device ID : 0060 Data Setting (decoded below) : 40 INITPass : 0 EIntPass : 0 NMIPass : 0 Reserved : 0 System MGMT : 0 LINT0 Pass : 1 LINT1 Pass : 0 ACPI HID : "MSFT0201" ACPI CID : 0000000000000000 UID Format : 02 UID Length : 09 UID : "_SB.MHSP" ```
SSDT: ``` Device (MHSP) { Name (_ADR, Zero) // _ADR: Address Name (_HID, "MSFT0201") // _HID: Hardware ID Name (_UID, One) // _UID: Unique ID ```
To handle this case; while enumerating ACPI devices in get_acpihid_device_id() count the number of matching ACPI devices with a matching _HID. If there is exactly one _HID match then accept it even if the UID doesn't match. Other operating systems allow this, but the current IVRS spec leaves some ambiguity whether to allow or disallow it. This should be clarified in future revisions of the spec. Output 'Firmware Bug' for this case to encourage it to be solved in the BIOS.
Signed-off-by: Mario Limonciello mario.limonciello@amd.com Reviewed-by: Vasant Hegde vasant.hegde@amd.com Link: https://lore.kernel.org/r/20250512173129.1274275-1-superm1@kernel.org Signed-off-by: Joerg Roedel jroedel@suse.de Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my analysis of the commit, the code changes, and the context from similar commits, here is my assessment: **YES** This commit should be backported to stable kernel trees for the following reasons: ## Bug Fix Analysis 1. **Real-world hardware compatibility issue**: The commit addresses a concrete problem where BIOS upgrades change IVRS DTE UIDs that no longer match the UIDs in SSDT, causing ACPI HID device matching to fail. This is a genuine hardware compatibility issue affecting real systems. 2. **Minimal, targeted change**: The modification is confined to a single function (`get_acpihid_device_id()`) in `drivers/iommu/amd/iommu.c`. The change adds fallback logic without altering the primary matching path, making it low-risk. 3. **Conservative approach**: The fix only allows UID mismatch when there's exactly one HID match (`hid_count == 1`), preventing ambiguous matches. It maintains strict validation by returning `-EINVAL` for multiple HID matches. 4. **Follows established patterns**: Similar to the reference commits (all marked "YES"), this addresses ACPI device matching issues in the AMD IOMMU subsystem, a pattern we've seen consistently backported. ## Code Change Analysis The modification transforms the original simple loop: ```c list_for_each_entry(p, &acpihid_map, list) { if (acpi_dev_hid_uid_match(adev, p->hid, p->uid[0] ? p->uid : NULL)) { if (entry) *entry = p; return p->devid; } } return -EINVAL; ``` Into a more robust matching algorithm that: - First attempts exact HID+UID matching (preserving original behavior) - Falls back to HID-only matching when exactly one device matches - Logs firmware bugs appropriately with `FW_BUG` - Rejects ambiguous multi-device scenarios ## Risk Assessment - **Low regression risk**: The primary matching path remains unchanged - **Backward compatibility**: Systems with correct BIOS behavior continue working identically - **Forward compatibility**: Handles broken BIOS scenarios gracefully - **Contained scope**: Changes are isolated to AMD IOMMU ACPI device identification ## Comparison with Reference Commits This commit follows the same pattern as the "YES" reference commits: - **Similar scope**: ACPI HID device matching in AMD IOMMU (like commits #1, #2, #3, #4) - **Bug fix nature**: Addresses real hardware compatibility issues - **Minimal code changes**: Small, contained modifications - **Critical subsystem**: IOMMU functionality is essential for system operation The commit contrasts with reference commit #5 (marked "NO") which introduced new kernel parameters - a feature addition rather than a bug fix. This commit represents exactly the type of important bug fix that stable kernels are designed to include: it resolves real-world hardware compatibility issues with minimal risk and follows established successful patterns in the same subsystem.
drivers/iommu/amd/iommu.c | 33 ++++++++++++++++++++++++++++----- 1 file changed, 28 insertions(+), 5 deletions(-)
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index f61e48f237324..4428a9557f295 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -107,7 +107,9 @@ static inline int get_acpihid_device_id(struct device *dev, struct acpihid_map_entry **entry) { struct acpi_device *adev = ACPI_COMPANION(dev); - struct acpihid_map_entry *p; + struct acpihid_map_entry *p, *p1 = NULL; + int hid_count = 0; + bool fw_bug;
if (!adev) return -ENODEV; @@ -115,12 +117,33 @@ static inline int get_acpihid_device_id(struct device *dev, list_for_each_entry(p, &acpihid_map, list) { if (acpi_dev_hid_uid_match(adev, p->hid, p->uid[0] ? p->uid : NULL)) { - if (entry) - *entry = p; - return p->devid; + p1 = p; + fw_bug = false; + hid_count = 1; + break; + } + + /* + * Count HID matches w/o UID, raise FW_BUG but allow exactly one match + */ + if (acpi_dev_hid_match(adev, p->hid)) { + p1 = p; + hid_count++; + fw_bug = true; } } - return -EINVAL; + + if (!p1) + return -EINVAL; + if (fw_bug) + dev_err_once(dev, FW_BUG "No ACPI device matched UID, but %d device%s matched HID.\n", + hid_count, hid_count > 1 ? "s" : ""); + if (hid_count > 1) + return -EINVAL; + if (entry) + *entry = p1; + + return p1->devid; }
static inline int get_device_sbdf_id(struct device *dev)