[v3,11/18] x86/mem_sharing: ASSERT that p2m_set_entry succeeds

Commit Message

Tamas K Lengyel Dec. 30, 2019, 4:11 p.m. UTC

Signed-off-by: Tamas K Lengyel <[e-mail]>
---
 xen/arch/x86/mm/mem_sharing.c | 42 +++++++++++++++++------------------
 1 file changed, 21 insertions(+), 21 deletions(-)

Patch

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 93e7605900..3f36cd6bbc 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1117,11 +1117,19 @@  int add_to_physmap(struct domain *sd, unsigned long sgfn, shr_handle_t sh,
         goto err_unlock;
     }
 
+    /*
+     * Must succeed, we just read the entry and hold the p2m lock
+     * via get_two_gfns.
+     */
     ret = p2m_set_entry(p2m, _gfn(cgfn), smfn, PAGE_ORDER_4K,
                         p2m_ram_shared, a);
+    ASSERT(!ret);
 
-    /* Tempted to turn this into an assert */
-    if ( ret )
+    /*
+     * There is a chance we're plugging a hole where a paged out
+     * page was.
+     */
+    if ( p2m_is_paging(cmfn_type) && (cmfn_type != p2m_ram_paging_out) )
     {
         mem_sharing_gfn_destroy(spage, cd, gfn_info);
         put_page_and_type(spage);
@@ -1129,29 +1137,21 @@  int add_to_physmap(struct domain *sd, unsigned long sgfn, shr_handle_t sh,
     else
     {
         /*
-         * There is a chance we're plugging a hole where a paged out
-         * page was.
+         * Further, there is a chance this was a valid page.
+         * Don't leak it.
          */
-        if ( p2m_is_paging(cmfn_type) && (cmfn_type != p2m_ram_paging_out) )
+        if ( mfn_valid(cmfn) )
         {
-            atomic_dec(&cd->paged_pages);
-            /*
-             * Further, there is a chance this was a valid page.
-             * Don't leak it.
-             */
-            if ( mfn_valid(cmfn) )
+            struct page_info *cpage = mfn_to_page(cmfn);
+
+            if ( !get_page(cpage, cd) )
             {
-                struct page_info *cpage = mfn_to_page(cmfn);
-
-                if ( !get_page(cpage, cd) )
-                {
-                    domain_crash(cd);
-                    ret = -EOVERFLOW;
-                    goto err_unlock;
-                }
-                put_page_alloc_ref(cpage);
-                put_page(cpage);
+                domain_crash(cd);
+                ret = -EOVERFLOW;
+                goto err_unlock;
             }
+            put_page_alloc_ref(cpage);
+            put_page(cpage);
         }
     }