x86/P2M: consolidate handling of types not requiring a valid MFN

As noted regarding the mixture of checks in p2m_pt_set_entry(),
introduce an new P2M type group allowing to be used everywhere we
just care about accepting operations with either a valid MFN or a type
permitting to be used without (valid) MFN.

Note that p2m_mmio_dm is not included in P2M_NO_MFN_TYPES, as for the
intended purpose that one ought to be treated similar to p2m_invalid
(perhaps the two should ultimately get folded anyway).

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

--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -780,8 +780,7 @@ ept_set_entry(struct p2m_domain *p2m, un
         ept_entry = table + (gfn_remainder >> (i * EPT_TABLE_ORDER));
     }
 
-    if ( mfn_valid(mfn_x(mfn)) || direct_mmio || p2m_is_paged(p2mt) ||
-         (p2mt == p2m_ram_paging_in) )
+    if ( mfn_valid(mfn_x(mfn)) || p2m_allows_invalid_mfn(p2mt) )
     {
         int emt = epte_get_entry_emt(p2m->domain, gfn, mfn,
                                      i * EPT_TABLE_ORDER, &ipat, direct_mmio);
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -753,7 +753,7 @@ p2m_pod_zero_check_superpage(struct p2m_
     }
 
     /* Try to remove the page, restoring old mapping if it fails. */
-    p2m_set_entry(p2m, gfn, _mfn(0), PAGE_ORDER_2M,
+    p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), PAGE_ORDER_2M,
                   p2m_populate_on_demand, p2m->default_access);
 
     /* Make none of the MFNs are used elsewhere... for example, mapped
@@ -869,7 +869,7 @@ p2m_pod_zero_check(struct p2m_domain *p2
         }
 
         /* Try to remove the page, restoring old mapping if it fails. */
-        p2m_set_entry(p2m, gfns[i], _mfn(0), PAGE_ORDER_4K,
+        p2m_set_entry(p2m, gfns[i], _mfn(INVALID_MFN), PAGE_ORDER_4K,
                       p2m_populate_on_demand, p2m->default_access);
 
         /* See if the page was successfully unmapped.  (Allow one refcount
@@ -1070,7 +1070,7 @@ p2m_pod_demand_populate(struct p2m_domai
          * NOTE: In a fine-grained p2m locking scenario this operation
          * may need to promote its locking from gfn->1g superpage
          */
-        p2m_set_entry(p2m, gfn_aligned, _mfn(0), PAGE_ORDER_2M,
+        p2m_set_entry(p2m, gfn_aligned, _mfn(INVALID_MFN), PAGE_ORDER_2M,
                       p2m_populate_on_demand, p2m->default_access);
         return 0;
     }
@@ -1152,7 +1152,7 @@ remap_and_retry:
      * need promoting the gfn lock from gfn->2M superpage */
     gfn_aligned = (gfn>>order)<<order;
     for(i=0; i<(1<<order); i++)
-        p2m_set_entry(p2m, gfn_aligned+i, _mfn(0), PAGE_ORDER_4K,
+        p2m_set_entry(p2m, gfn_aligned + i, _mfn(INVALID_MFN), PAGE_ORDER_4K,
                       p2m_populate_on_demand, p2m->default_access);
     if ( tb_init_done )
     {
@@ -1210,8 +1210,8 @@ guest_physmap_mark_populate_on_demand(st
     }
 
     /* Now, actually do the two-way mapping */
-    rc = p2m_set_entry(p2m, gfn, _mfn(0), order, p2m_populate_on_demand,
-                       p2m->default_access);
+    rc = p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), order,
+                       p2m_populate_on_demand, p2m->default_access);
     if ( rc == 0 )
     {
         pod_lock(p2m);
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -571,7 +571,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m,
         }
 
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
-        l3e_content = mfn_valid(mfn) 
+        l3e_content = mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt)
             ? l3e_from_pfn(mfn_x(mfn),
                            p2m_type_to_flags(p2mt, mfn) | _PAGE_PSE)
             : l3e_empty();
@@ -607,8 +607,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m,
             p2m_get_iommu_flags(p2m_flags_to_type(l1e_get_flags(*p2m_entry)));
         old_mfn = l1e_get_pfn(*p2m_entry);
 
-        if ( mfn_valid(mfn) || (p2mt == p2m_mmio_direct)
-                            || p2m_is_paging(p2mt) )
+        if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             entry_content = p2m_l1e_from_pfn(mfn_x(mfn),
                                              p2m_type_to_flags(p2mt, mfn));
         else
@@ -644,7 +643,7 @@ p2m_pt_set_entry(struct p2m_domain *p2m,
         }
         
         ASSERT(!mfn_valid(mfn) || p2mt != p2m_mmio_direct);
-        if ( mfn_valid(mfn) || p2m_is_pod(p2mt) )
+        if ( mfn_valid(mfn) || p2m_allows_invalid_mfn(p2mt) )
             l2e_content = l2e_from_pfn(mfn_x(mfn),
                                        p2m_type_to_flags(p2mt, mfn) |
                                        _PAGE_PSE);
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -141,6 +141,11 @@ typedef unsigned int p2m_query_t;
                             | p2m_to_mask(p2m_ram_logdirty) )
 #define P2M_SHARED_TYPES   (p2m_to_mask(p2m_ram_shared))
 
+/* Valid types not necessarily associated with a (valid) MFN. */
+#define P2M_INVALID_MFN_TYPES (P2M_POD_TYPES                  \
+                               | p2m_to_mask(p2m_mmio_direct) \
+                               | P2M_PAGING_TYPES)
+
 /* Broken type: the frame backing this pfn has failed in hardware
  * and must not be touched. */
 #define P2M_BROKEN_TYPES (p2m_to_mask(p2m_ram_broken))
@@ -171,6 +176,8 @@ typedef unsigned int p2m_query_t;
                              (P2M_RAM_TYPES | P2M_GRANT_TYPES |  \
                               p2m_to_mask(p2m_map_foreign)))
 
+#define p2m_allows_invalid_mfn(t) (p2m_to_mask(t) & P2M_INVALID_MFN_TYPES)
+
 typedef enum {
     p2m_host,
     p2m_nested,