x86/HVM: restrict HVMOP_set_mem_type

Permitting arbitrary type changes here has the potential of creating
present P2M (and hence EPT/NPT/IOMMU) entries pointing to an invalid
MFN (INVALID_MFN truncated to the respective hardware structure field's
width). This would become a problem the latest when something real sat
at the end of the physical address space; I'm suspecting though that
other things might break with such bogus entries.

Along with that drop a bogus (and otherwise becoming stale) log
message.

Afaict the similar operation in p2m_set_mem_access() is safe.

This is XSA-92.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3666,13 +3666,9 @@ long do_hvm_op(unsigned long op, XEN_GUE
                 rc = -EINVAL;
                 goto param_fail4;
             } 
-            if ( p2m_is_grant(t) )
-            {
-                gdprintk(XENLOG_WARNING,
-                         "type for pfn 0x%lx changed to grant while "
-                         "we were working?\n", pfn);
+            if ( !p2m_is_ram(t) &&
+                 (!p2m_is_hole(t) || a.hvmmem_type != HVMMEM_mmio_dm) )
                 goto param_fail4;
-            }
             else
             {
                 nt = p2m_change_type(p2m, pfn, t, memtype[a.hvmmem_type]);
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -134,6 +134,13 @@ typedef enum {
                        | p2m_to_mask(p2m_ram_paging_in)       \
                        | p2m_to_mask(p2m_ram_shared))
 
+/* Types that represent a physmap hole. */
+#define P2M_HOLE_TYPES (p2m_to_mask(p2m_mmio_dm)               \
+                        | p2m_to_mask(p2m_invalid)             \
+                        | p2m_to_mask(p2m_ram_paging_in_start) \
+                        | p2m_to_mask(p2m_ram_paging_in)       \
+                        | p2m_to_mask(p2m_ram_paged))
+
 /* Grant mapping types, which map to a real machine frame in another
  * VM */
 #define P2M_GRANT_TYPES (p2m_to_mask(p2m_grant_map_rw)  \
@@ -170,6 +177,7 @@ typedef enum {
 
 /* Useful predicates */
 #define p2m_is_ram(_t) (p2m_to_mask(_t) & P2M_RAM_TYPES)
+#define p2m_is_hole(_t) (p2m_to_mask(_t) & P2M_HOLE_TYPES)
 #define p2m_is_mmio(_t) (p2m_to_mask(_t) & P2M_MMIO_TYPES)
 #define p2m_is_readonly(_t) (p2m_to_mask(_t) & P2M_RO_TYPES)
 #define p2m_is_magic(_t) (p2m_to_mask(_t) & P2M_MAGIC_TYPES)