[PATCH v2 1/3] iommu/amd: Prevent SB IOAPIC from overriding IVRS validation errors

[Wei Wang]

The check_ioapic_information() function validates IOAPICs against the
IVRS table to safely disable Interrupt Remapping (IR) if the BIOS provides
a broken topology.

Currently, the validation loop contains a bug: If an unmapped secondary
IOAPIC is encountered, 'ret' is set to false. But if the Southbridge (SB)
IOAPIC is enumerated after it in the MADT, the loop overwrites 'ret' to
true.

This bypasses the validation failure and leaves IR enabled. When devices
attached to the unmapped secondary IOAPIC fire interrupts, the IOMMU drops
them due to the missing Requestor ID, leading to localized device hangs.

Fix this by initializing 'ret' to true and only toggling it to false
upon encountering a validation error, ensuring failures are never erased.

Fixes: c2ff5cf5294b ("iommu/amd: Work around wrong IOAPIC device-id in IVRS table")
Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxxxx>
Tested-by: Yongwei Xu <xuyongwei@xxxxxxxxxxxxxx>
Reviewed-by: Vasant Hegde <vasant.hegde@xxxxxxx>
---
 drivers/iommu/amd/init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index e93bcb5eef70..f983b1961847 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3098,7 +3098,7 @@ static bool __init check_ioapic_information(void)
 	int idx;
 
 	has_sb_ioapic = false;
-	ret           = false;
+	ret           = true;
 
 	/*
 	 * If we have map overrides on the kernel command line the
@@ -3123,7 +3123,6 @@ static bool __init check_ioapic_information(void)
 			    boot_cpu_data.x86_model <= 0xf &&
 			    devid == IOAPIC_SB_DEVID_FAM18H_M4H)) {
 			has_sb_ioapic = true;
-			ret           = true;
 		}
 	}
 
@@ -3137,6 +3136,7 @@ static bool __init check_ioapic_information(void)
 		 * device id for the IOAPIC in the system.
 		 */
 		pr_err("%s: No southbridge IOAPIC found\n", fw_bug);
+		ret = false;
 	}
 
 	if (!ret)
-- 
2.51.0