x86/mm: make free_perdomain_mappings() idempotent

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 77b0af1f9e5df9ccf041be6bb6c9dbbf3b9f4039..411eed0d0a4dd300ddcf821cd0624dbd7e10b624 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -6514,9 +6514,14 @@ void destroy_perdomain_mapping(struct domain *d, unsigned long va,
 
 void free_perdomain_mappings(struct domain *d)
 {
-    l3_pgentry_t *l3tab = __map_domain_page(d->arch.perdomain_l3_pg);
+    l3_pgentry_t *l3tab;
     unsigned int i;
 
+    if ( !d->arch.perdomain_l3_pg )
+        return;
+
+    l3tab = __map_domain_page(d->arch.perdomain_l3_pg);
+
     for ( i = 0; i < PERDOMAIN_SLOTS; ++i)
         if ( l3e_get_flags(l3tab[i]) & _PAGE_PRESENT )
         {
@@ -6555,6 +6560,7 @@ void free_perdomain_mappings(struct domain *d)
 
     unmap_domain_page(l3tab);
     free_domheap_page(d->arch.perdomain_l3_pg);
+    d->arch.perdomain_l3_pg = NULL;
 }
 
 #ifdef MEMORY_GUARD