[Xen-devel] [PATCH v2] 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.

Unfortunately (partially) replacing the iommu_map() call in
iommu_hwdom_init() implies resurrecting the flush suppression that got
previously eliminated. Note that the call to iommu_map() can't be
removed at this point in time - Dom0's initial allocation gets its page
types set before iommu_hwdom_init() runs.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Fix IOTLB flushing. Exclude PVH. Use type safe local variables.

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -873,11 +873,11 @@ 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
@@ -192,28 +192,46 @@ void __hwdom_init iommu_hwdom_init(struc
         unsigned int i = 0, flush_flags = 0;
         int rc = 0;
 
+        this_cpu(iommu_dont_flush_iotlb) = true;
+
         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_count_mask) == 0) ||
-                 ((page->u.inuse.type_info & PGT_type_mask)
-                  == PGT_writable_page) )
-                mapping |= IOMMUF_writable;
-
-            ret = iommu_map(d, _dfn(dfn), _mfn(mfn), 0, mapping,
-                            &flush_flags);
-
-            if ( !rc )
-                rc = ret;
+            switch ( page->u.inuse.type_info & PGT_type_mask )
+            {
+            case PGT_none:
+                if ( is_pv_domain(d) )
+                {
+                    ASSERT(!(page->u.inuse.type_info & PGT_count_mask));
+                    if ( get_page_and_type(page, d, PGT_writable_page) )
+                    {
+                        put_page_and_type(page);
+                        flush_flags |= IOMMUF_readable | IOMMUF_writable;
+                    }
+                    else if ( !rc )
+                        rc = -EBUSY;
+                    break;
+                }
+                /* fall through */
+            case PGT_writable_page:
+            {
+                mfn_t mfn = page_to_mfn(page);
+                dfn_t dfn = _dfn(mfn_to_gmfn(d, mfn_x(mfn)));
+                int ret = iommu_map(d, dfn, mfn, 0,
+                                    IOMMUF_readable | IOMMUF_writable,
+                                    &flush_flags);
+
+                if ( !rc )
+                    rc = ret;
+                break;
+            }
+            }
 
             if ( !(i++ & 0xfffff) )
                 process_pending_softirqs();
         }
 
+        this_cpu(iommu_dont_flush_iotlb) = false;
+
         /* Use while-break to avoid compiler warning */
         while ( iommu_iotlb_flush_all(d, flush_flags) )
             break;




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