intel-iommu: Fix kernel hang if interrupt remapping disabled in BIOS

BIOS clear DMAR table INTR_REMAP flag to disable interrupt remapping. Current
kernel only check interrupt remapping(IR) flag in DRHD's extended capability
register to decide interrupt remapping support or not. But IR flag will not
change when BIOS disable/enable interrupt remapping.

When user disable interrupt remapping in BIOS or BIOS often defaultly disable
interrupt remapping feature when BIOS is not mature.Though BIOS disable
interrupt remapping but intr_remapping_supported function will always report
to OS support interrupt remapping if VT-d2 chipset populated. On this
cases, kernel will continue enable interrupt remapping and result kernel panic.
This bug exist on almost all platforms with interrupt remapping support.

This patch add DMAR table INTR_REMAP flag check before enable interrupt
remapping.

Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
index fba4f68..270ed22 100644
--- a/drivers/pci/dmar.c
+++ b/drivers/pci/dmar.c
@@ -1316,3 +1316,13 @@ int dmar_reenable_qi(struct intel_iommu *iommu)
 
 	return 0;
 }
+
+/*
+ * Check interrupt remapping support in DMAR table description.
+ */
+int dmar_ir_support(void)
+{
+	struct acpi_table_dmar *dmar;
+	dmar = (struct acpi_table_dmar *)dmar_tbl;
+	return dmar->flags & 0x1;
+}