[Xen-devel] [PATCH 2/3] IOMMU/x86: make page type checks consistent when mapping pages

["Jan Beulich" <JBeulich@xxxxxxxx>]

There are currently three more or less different checks:
- _get_page_type() adjusts the IOMMU mappings according to the new type
  alone,
- arch_iommu_populate_page_table() wants just the type to be
  PGT_writable_page,
- iommu_hwdom_init() additionally permits all other types with a type
  refcount of zero.
The canonical one is in _get_page_type(), and as of XSA-288
arch_iommu_populate_page_table() also has no need anymore to deal with
PGT_none pages. In the PV Dom0 case, however, PGT_none pages are still
necessary to consider, since in that case pages don't get handed to
guest_physmap_add_entry(). Furthermore, the function so far also
established r/o mappings, which is not in line with the rules set forth
by the XSA-288 change.

For arch_iommu_populate_page_table() to not encounter PGT_none pages
anymore even in cases where the IOMMU gets enabled for a domain only
when it is already running, replace the IOMMU dependency in
guest_physmap_add_entry()'s handling of PV guests to check just the
system wide state instead of the domain property.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -837,11 +837,11 @@ guest_physmap_add_entry(struct domain *d
          *
          * Retain this property by grabbing a writable type ref and then
          * dropping it immediately.  The result will be pages that have a
-         * writable type (and an IOMMU entry), but a count of 0 (such that
-         * any guest-requested type changes succeed and remove the IOMMU
-         * entry).
+         * writable type (and an IOMMU entry if necessary), but a count of 0
+         * (such that any guest-requested type changes succeed and remove the
+         * IOMMU entry).
          */
-        if ( !need_iommu_pt_sync(d) || t != p2m_ram_rw )
+        if ( !iommu_enabled || t != p2m_ram_rw )
             return 0;
 
         for ( i = 0; i < (1UL << page_order); ++i, ++page )
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -192,21 +192,27 @@ void __hwdom_init iommu_hwdom_init(struc
 
         page_list_for_each ( page, &d->page_list )
         {
-            unsigned long mfn = mfn_x(page_to_mfn(page));
-            unsigned long dfn = mfn_to_gmfn(d, mfn);
-            unsigned int mapping = IOMMUF_readable;
-            int ret;
+            if ( (page->u.inuse.type_info & PGT_type_mask) == PGT_none )
+            {
+                ASSERT(!(page->u.inuse.type_info & PGT_count_mask));
+                if ( get_page_and_type(page, d, PGT_writable_page) )
+                    put_page_and_type(page);
+                else if ( !rc )
+                    rc = -EBUSY;
+            }
 
-            if ( ((page->u.inuse.type_info & PGT_count_mask) == 0) ||
-                 ((page->u.inuse.type_info & PGT_type_mask)
-                  == PGT_writable_page) )
-                mapping |= IOMMUF_writable;
+            if ( ((page->u.inuse.type_info & PGT_type_mask) ==
+                  PGT_writable_page) )
+            {
+                unsigned long mfn = mfn_x(page_to_mfn(page));
+                unsigned long dfn = mfn_to_gmfn(d, mfn);
+                int ret = iommu_map(d, _dfn(dfn), _mfn(mfn), 0,
+                                    IOMMUF_readable | IOMMUF_writable,
+                                    &flush_flags);
 
-            ret = iommu_map(d, _dfn(dfn), _mfn(mfn), 0, mapping,
-                            &flush_flags);
-
-            if ( !rc )
-                rc = ret;
+                if ( !rc )
+                    rc = ret;
+            }
 
             if ( !(i++ & 0xfffff) )
                 process_pending_softirqs();





_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel