[Xen-devel] [PATCH] amd-iommu: Fix Guest CR3 Table following c/s 3a7947b6901

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

"amd-iommu: use a bitfield for DTE" renamed iommu_dte_set_guest_cr3()'s gcr3
parameter to gcr3_mfn but ended up with an off-by-PAGE_SIZE error when
extracting bits from the address.

First of all, get_guest_cr3_from_dte() and iommu_dte_set_guest_cr3()
are (almost) getters and setters for the same field, so should live together.

Rename them to dte_{get,set}_gcr3_table() to specifically avoid 'guest_cr3' in
the name.  This field actually points to a table in memory containing an array
of guest CR3 values.  As these functions are used for different logical
indirections, they shouldn't use gfn/mfn terminology for their parameters.
Switch them to use straight uint64_t full addresses.

Finally, correct the dte_set_gcr3_table() to use the proper shift.  Express
the shifts visually using MASK_EXTR() and literal masks, which IMO is the
clearest way to express the logic.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Brian Woods <brian.woods@xxxxxxx>
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>

This code is unreachable, so completely untestable, but I think the end result
is better than it was previously.
---
 xen/drivers/passthrough/amd/iommu_guest.c     | 32 +++++++++++++++++++++++----
 xen/drivers/passthrough/amd/iommu_map.c       | 21 ------------------
 xen/include/asm-x86/hvm/svm/amd-iommu-proto.h |  2 --
 3 files changed, 28 insertions(+), 27 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu_guest.c 
b/xen/drivers/passthrough/amd/iommu_guest.c
index 328e750..4691e8f 100644
--- a/xen/drivers/passthrough/amd/iommu_guest.c
+++ b/xen/drivers/passthrough/amd/iommu_guest.c
@@ -76,10 +76,34 @@ static void guest_iommu_disable(struct guest_iommu *iommu)
     iommu->enabled = 0;
 }
 
-static uint64_t get_guest_cr3_from_dte(struct amd_iommu_dte *dte)
+/*
+ * The Guest CR3 Table is a table written by the guest kernel, pointing at
+ * gCR3 values for PASID transactions to use.  The Device Table Entry points
+ * at a system physical address.
+ *
+ * However, these helpers deliberately use untyped parameters without
+ * reference to gfn/mfn because they are used both for programming the real
+ * IOMMU, and interpreting a guests programming of its vIOMMU.
+ */
+static uint64_t dte_get_gcr3_table(const struct amd_iommu_dte *dte)
 {
     return ((dte->gcr3_trp_51_31 << 31) | (dte->gcr3_trp_30_15 << 15) |
-            (dte->gcr3_trp_14_12 << 12)) >> PAGE_SHIFT;
+            (dte->gcr3_trp_14_12 << 12));
+}
+
+static void dte_set_gcr3_table(struct amd_iommu_dte *dte, uint16_t dom_id,
+                               uint64_t addr, uint8_t gv, uint8_t glx)
+{
+    /* I bit must be set when gcr3 is enabled */
+    dte->i = 1;
+
+    dte->gcr3_trp_14_12 = MASK_EXTR(addr, 0x0000000000007000ull);
+    dte->gcr3_trp_30_15 = MASK_EXTR(addr, 0x000000007fff8000ull);
+    dte->gcr3_trp_51_31 = MASK_EXTR(addr, 0x000fffff80000000ull);
+
+    dte->domain_id = dom_id;
+    dte->glx = glx;
+    dte->gv = gv;
 }
 
 static unsigned int host_domid(struct domain *d, uint64_t g_domid)
@@ -399,7 +423,7 @@ static int do_invalidate_dte(struct domain *d, cmd_entry_t 
*cmd)
     gdte = &dte_base[gbdf % (PAGE_SIZE / sizeof(struct amd_iommu_dte))];
 
     gdom_id = gdte->domain_id;
-    gcr3_gfn = get_guest_cr3_from_dte(gdte);
+    gcr3_gfn = dte_get_gcr3_table(gdte) >> PAGE_SHIFT;
     glx = gdte->glx;
     gv = gdte->gv;
 
@@ -429,7 +453,7 @@ static int do_invalidate_dte(struct domain *d, cmd_entry_t 
*cmd)
     mdte = &dte_base[req_id];
 
     spin_lock_irqsave(&iommu->lock, flags);
-    iommu_dte_set_guest_cr3(mdte, hdom_id, gcr3_mfn, gv, glx);
+    dte_set_gcr3_table(mdte, hdom_id, gcr3_mfn << PAGE_SHIFT, gv, glx);
 
     amd_iommu_flush_device(iommu, req_id);
     spin_unlock_irqrestore(&iommu->lock, flags);
diff --git a/xen/drivers/passthrough/amd/iommu_map.c 
b/xen/drivers/passthrough/amd/iommu_map.c
index cbf00e9..32a8fdc 100644
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -138,27 +138,6 @@ void __init iommu_dte_add_device_entry(struct 
amd_iommu_dte *dte,
     dte->ex = ivrs_dev->dte_allow_exclusion;
 }
 
-void iommu_dte_set_guest_cr3(struct amd_iommu_dte *dte, uint16_t dom_id,
-                             uint64_t gcr3_mfn, uint8_t gv, uint8_t glx)
-{
-#define GCR3_MASK(hi, lo) (((1ul << ((hi) + 1)) - 1) & ~((1ul << (lo)) - 1))
-#define GCR3_SHIFT(lo) ((lo) - PAGE_SHIFT)
-
-    /* I bit must be set when gcr3 is enabled */
-    dte->i = 1;
-
-    dte->gcr3_trp_14_12 = (gcr3_mfn & GCR3_MASK(14, 12)) >> GCR3_SHIFT(12);
-    dte->gcr3_trp_30_15 = (gcr3_mfn & GCR3_MASK(30, 15)) >> GCR3_SHIFT(15);
-    dte->gcr3_trp_51_31 = (gcr3_mfn & GCR3_MASK(51, 31)) >> GCR3_SHIFT(31);
-
-    dte->domain_id = dom_id;
-    dte->glx = glx;
-    dte->gv = gv;
-
-#undef GCR3_SHIFT
-#undef GCR3_MASK
-}
-
 /* Walk io page tables and build level page tables if necessary
  * {Re, un}mapping super page frames causes re-allocation of io
  * page tables.
diff --git a/xen/include/asm-x86/hvm/svm/amd-iommu-proto.h 
b/xen/include/asm-x86/hvm/svm/amd-iommu-proto.h
index e0d5d23..c6179dc 100644
--- a/xen/include/asm-x86/hvm/svm/amd-iommu-proto.h
+++ b/xen/include/asm-x86/hvm/svm/amd-iommu-proto.h
@@ -79,8 +79,6 @@ void amd_iommu_set_root_page_table(struct amd_iommu_dte *dte,
                                   uint8_t paging_mode, uint8_t valid);
 void iommu_dte_add_device_entry(struct amd_iommu_dte *dte,
                                 struct ivrs_mappings *ivrs_dev);
-void iommu_dte_set_guest_cr3(struct amd_iommu_dte *dte, uint16_t dom_id,
-                             uint64_t gcr3_mfn, uint8_t gv, uint8_t glx);
 
 /* send cmd to iommu */
 void amd_iommu_flush_all_pages(struct domain *d);
-- 
2.1.4


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