[PATCH] iommu/vt-d: Fix UCTP context table slot when copying root entries

[Desnes Nunes <desnesn@redhat.com>]

When translation is already enabled at boot (e.g. kdump), the vt-d driver
copies context tables from the previous kernel's root table. In scalable
mode, buses that only populate the upper root half (UCTP, devfn >= 0x80)
should be written to ctxt_tbls[tbl_idx + 1] through copy_context_table().
However, the current copy path always uses tbl[tbl_idx + 0] in this situa-
tion. Since idx wraps to 0 at devfn 0x80 due to a zeroed LCTP, new_ce for
LCTP will be NULL and keep pos equals to 0. Thus, UCTP entries will be co-
pied into tbl[tbl_idx + 0] instead of tbl[tbl_idx + 1], and written after-
wards to root_entry[bus].lo instead of .hi in copy_translation_tables().

As consequence, devices on bus 0x80 with devfn >= 0x80 fail DMA with
fault 0x39, which breaks drivers running in kernels with translation
pre-enabled. This fixes NO_PASID DMAR faults for UCTP-only buses such as:

DMAR: [DMA Read NO_PASID] Request device [80:14.0] fault addr 0xe81759000 [fault reason 0x39] SM: Present bit in Root Entry is clear

Fixes: 091d42e43d21 ("iommu/vt-d: Copy translation tables from old kernel")
Signed-off-by: Desnes Nunes <desnesn@redhat.com>
---
 drivers/iommu/intel/iommu.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 4d0e65bc131d..737936f942a0 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1443,7 +1443,7 @@ static int copy_context_table(struct intel_iommu *iommu,
 			      struct context_entry **tbl,
 			      int bus, bool ext)
 {
-	int tbl_idx, pos = 0, idx, devfn, ret = 0, did;
+	int tbl_idx, tbl_slot = 0, idx, devfn, ret = 0, did;
 	struct context_entry *new_ce = NULL, ce;
 	struct context_entry *old_ce = NULL;
 	struct root_entry re;
@@ -1459,10 +1459,9 @@ static int copy_context_table(struct intel_iommu *iommu,
 		if (idx == 0) {
 			/* First save what we may have and clean up */
 			if (new_ce) {
-				tbl[tbl_idx] = new_ce;
+				tbl[tbl_idx + tbl_slot] = new_ce;
 				__iommu_flush_cache(iommu, new_ce,
 						    VTD_PAGE_SIZE);
-				pos = 1;
 			}
 
 			if (old_ce)
@@ -1484,6 +1483,9 @@ static int copy_context_table(struct intel_iommu *iommu,
 				}
 			}
 
+			/* Track if saving UCTP or LCTP entries in scalable mode */
+			tbl_slot = ext && devfn >= 0x80 ? 1 : 0;
+
 			ret = -ENOMEM;
 			old_ce = memremap(old_ce_phys, PAGE_SIZE,
 					MEMREMAP_WB);
@@ -1512,7 +1514,7 @@ static int copy_context_table(struct intel_iommu *iommu,
 		new_ce[idx] = ce;
 	}
 
-	tbl[tbl_idx + pos] = new_ce;
+	tbl[tbl_idx + tbl_slot] = new_ce;
 
 	__iommu_flush_cache(iommu, new_ce, VTD_PAGE_SIZE);
 
-- 
2.54.0