[PATCH 1/2] x86/p2m: make p2m_get_page_from_gfn() handle grant and shared cases better

[Jan Beulich <jbeulich@xxxxxxxx>]

Grant P2M entries, which are covered by p2m_is_any_ram(), wouldn't pass
the get_page() unless the grant was a local one. These need to take the
same path as foreign entries. Just the assertion there is not valid for
local grants, and hence it triggering needs to be avoided.

Shared entries, when unshare is requested, would bypass the retrieval of
"page" and thus always take the error path rather than actually trying
to unshare by taking the slow path.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Using | instead of || helps the compiler fold the two p2m_is_*().

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -584,11 +584,11 @@ struct page_info *p2m_get_page_from_gfn(
              && !((q & P2M_UNSHARE) && p2m_is_shared(*t)) )
         {
             page = mfn_to_page(mfn);
-            if ( unlikely(p2m_is_foreign(*t)) )
+            if ( unlikely(p2m_is_foreign(*t) | p2m_is_grant(*t)) )
             {
                 struct domain *fdom = page_get_owner_and_reference(page);
 
-                ASSERT(fdom != p2m->domain);
+                ASSERT(!p2m_is_foreign(*t) || fdom != p2m->domain);
                 if ( fdom == NULL )
                     page = NULL;
             }
@@ -607,6 +607,7 @@ struct page_info *p2m_get_page_from_gfn(
 
         /* Error path: not a suitable GFN at all */
         if ( !p2m_is_ram(*t) && !p2m_is_paging(*t) && !p2m_is_pod(*t) &&
+             (!p2m_is_shared(*t) || !(q & P2M_UNSHARE)) &&
              !mem_sharing_is_fork(p2m->domain) )
             return NULL;
     }