This reverts commit ab96746aaa344fb720a198245a837e266fad3b62.
The commit ab96746aaa34 ("iommu/vt-d: Clean up pasid quirk for
pre-production devices") triggers ECS mode on some platforms
which have broken ECS support. As the result, graphic device
will be inoperable on boot.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107017
Cc: Ashok Raj
Signed-off-by: Lu Baolu
---
drivers/iommu/intel-iommu.c | 32 ++--
include/linux/intel-iommu.h | 1 +
2 files changed, 31 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index b344a88..115ff26 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -484,14 +484,37 @@ static int dmar_forcedac;
static int intel_iommu_strict;
static int intel_iommu_superpage = 1;
static int intel_iommu_ecs = 1;
+static int intel_iommu_pasid28;
static int iommu_identity_mapping;
#define IDENTMAP_ALL 1
#define IDENTMAP_GFX 2
#define IDENTMAP_AZALIA4
-#define ecs_enabled(iommu) (intel_iommu_ecs && ecap_ecs(iommu->ecap))
-#define pasid_enabled(iommu) (ecs_enabled(iommu) && ecap_pasid(iommu->ecap))
+/* Broadwell and Skylake have broken ECS support — normal so-called "second
+ * level" translation of DMA requests-without-PASID doesn't actually happen
+ * unless you also set the NESTE bit in an extended context-entry. Which of
+ * course means that SVM doesn't work because it's trying to do nested
+ * translation of the physical addresses it finds in the process page tables,
+ * through the IOVA->phys mapping found in the "second level" page tables.
+ *
+ * The VT-d specification was retroactively changed to change the definition
+ * of the capability bits and pretend that Broadwell/Skylake never happened...
+ * but unfortunately the wrong bit was changed. It's ECS which is broken, but
+ * for some reason it was the PASID capability bit which was redefined (from
+ * bit 28 on BDW/SKL to bit 40 in future).
+ *
+ * So our test for ECS needs to eschew those implementations which set the old
+ * PASID capabiity bit 28, since those are the ones on which ECS is broken.
+ * Unless we are working around the 'pasid28' limitations, that is, by putting
+ * the device into passthrough mode for normal DMA and thus masking the bug.
+ */
+#define ecs_enabled(iommu) (intel_iommu_ecs && ecap_ecs(iommu->ecap) && \
+ (intel_iommu_pasid28 ||
!ecap_broken_pasid(iommu->ecap)))
+/* PASID support is thus enabled if ECS is enabled and *either* of the old
+ * or new capability bits are set. */
+#define pasid_enabled(iommu) (ecs_enabled(iommu) &&\
+ (ecap_pasid(iommu->ecap) ||
ecap_broken_pasid(iommu->ecap)))
int intel_iommu_gfx_mapped;
EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped);
@@ -554,6 +577,11 @@ static int __init intel_iommu_setup(char *str)
printk(KERN_INFO
"Intel-IOMMU: disable extended context table
support\n");
intel_iommu_ecs = 0;
+ } else if (!strncmp(str, "pasid28", 7)) {
+ printk(KERN_INFO
+ "Intel-IOMMU: enable pre-production PASID
support\n");
+ intel_iommu_pasid28 = 1;
+ iommu_identity_mapping |= IDENTMAP_GFX;
} else if (!strncmp(str, "tboot_noforce", 13)) {
printk(KERN_INFO
"Intel-IOMMU: not forcing on after tboot. This
could expose security risk for tboot\n");
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 1df9401..ef169d6 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -121,6 +121,7 @@
#define ecap_srs(e)((e >> 31) & 0x1)
#define ecap_ers(e)((e >> 30) & 0x1)
#define ecap_prs(e)((e >> 29) & 0x1)
+#define ecap_broken_pasid(e) ((e >> 28) & 0x1)
#define ecap_dis(e)((e >> 27) & 0x1)
#define ecap_nest(e) ((e >> 26) & 0x1)
#define ecap_mts(e)((e >> 25) & 0x1)
--
2.7.4
___
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
