partially revert "x86/mm: Clean IOMMU flags from p2m-pt code"

This partially reverts commit
854a49a748 by re-adding the logic that
propagates changes to the domain physmap done by p2m_pt_set_entry into
the iommu page tables. Without this logic changes to the guest physmap
are not propagated to the iommu, leaving stale iommu entries that can
leak data, or failing to add new entries.

Note that this commit doesn't re-introduce iommu flags to the cpu page
table entries, since the logic to add/remove entries to the iommu page
tables is based on the p2m type and the mfn.

Fixes: 854a49a748 ('x86/mm: Clean IOMMU flags from p2m-pt code')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Alexandru Isaila <aisaila@bitdefender.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>

xen/arch/x86/mm/p2m-pt.c

@@ -508,7 +508,18 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, mfn_t mfn,
     l2_pgentry_t l2e_content;
     l3_pgentry_t l3e_content;
     int rc;
-    unsigned int flags;
+    unsigned int iommu_pte_flags = p2m_get_iommu_flags(p2mt, mfn);
+    /*
+     * old_mfn and iommu_old_flags control possible flush/update needs on the
+     * IOMMU: We need to flush when MFN or flags (i.e. permissions) change.
+     * iommu_old_flags being initialized to zero covers the case of the entry
+     * getting replaced being a non-present (leaf or intermediate) one. For
+     * present leaf entries the real value will get calculated below, while
+     * for present intermediate entries ~0 (guaranteed != iommu_pte_flags)
+     * will be used (to cover all cases of what the leaf entries underneath
+     * the intermediate one might be).
+     */
+    unsigned int flags, iommu_old_flags = 0;
     unsigned long old_mfn = mfn_x(INVALID_MFN);
 
     if ( !sve )
@@ -556,9 +567,17 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, mfn_t mfn,
         if ( flags & _PAGE_PRESENT )
         {
             if ( flags & _PAGE_PSE )
+            {
                 old_mfn = l1e_get_pfn(*p2m_entry);
+                iommu_old_flags =
+                    p2m_get_iommu_flags(p2m_flags_to_type(flags),
+                                        _mfn(old_mfn));
+            }
             else
+            {
+                iommu_old_flags = ~0;
                 intermediate_entry = *p2m_entry;
+            }
         }
 
         check_entry(mfn, p2mt, p2m_flags_to_type(flags), page_order);
@@ -594,6 +613,9 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, mfn_t mfn,
                                    0, L1_PAGETABLE_ENTRIES);
         ASSERT(p2m_entry);
         old_mfn = l1e_get_pfn(*p2m_entry);
+        iommu_old_flags =
+            p2m_get_iommu_flags(p2m_flags_to_type(l1e_get_flags(*p2m_entry)),
+                                _mfn(old_mfn));
 
         if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             entry_content = p2m_l1e_from_pfn(mfn_x(mfn),
@@ -617,9 +639,17 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, mfn_t mfn,
         if ( flags & _PAGE_PRESENT )
         {
             if ( flags & _PAGE_PSE )
+            {
                 old_mfn = l1e_get_pfn(*p2m_entry);
+                iommu_old_flags =
+                    p2m_get_iommu_flags(p2m_flags_to_type(flags),
+                                        _mfn(old_mfn));
+            }
             else
+            {
+                iommu_old_flags = ~0;
                 intermediate_entry = *p2m_entry;
+            }
         }
 
         check_entry(mfn, p2mt, p2m_flags_to_type(flags), page_order);
@@ -640,9 +670,17 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, mfn_t mfn,
          && (gfn + (1UL << page_order) - 1 > p2m->max_mapped_pfn) )
         p2m->max_mapped_pfn = gfn + (1UL << page_order) - 1;
 
+    if ( need_iommu_pt_sync(p2m->domain) &&
+         (iommu_old_flags != iommu_pte_flags || old_mfn != mfn_x(mfn)) )
+        rc = iommu_pte_flags
+             ? iommu_legacy_map(d, _dfn(gfn), mfn, page_order,
+                                iommu_pte_flags)
+             : iommu_legacy_unmap(d, _dfn(gfn), page_order);
+
     /*
      * Free old intermediate tables if necessary.  This has to be the
-     * last thing we do so as to avoid a potential use-after-free.
+     * last thing we do, after removal from the IOMMU tables, so as to
+     * avoid a potential use-after-free.
      */
     if ( l1e_get_flags(intermediate_entry) & _PAGE_PRESENT )
         p2m_free_entry(p2m, &intermediate_entry, page_order);