[Xen-devel] [PATCH] x86: put_page_from_l2e() should honor _PAGE_RW

["Jan Beulich" <JBeulich@xxxxxxxx>]

56fff3e5e9 ("x86: nuke PV superpage option and code") has introduced a
(luckily latent only) bug here, in that it didn't make reference
dropping dependent on whether the page was mapped writable. The only
current source of large page mappings for PV domains is the Dom0
builder, which only produces writeable ones.

Take the opportunity and also convert to bool both put_data_page()'s
respective parameter and the argument put_page_from_l3e() passes.

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

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -663,8 +663,7 @@ static int get_page_and_type_from_mfn(
     return rc;
 }
 
-static void put_data_page(
-    struct page_info *page, int writeable)
+static void put_data_page(struct page_info *page, bool writeable)
 {
     if ( writeable )
         put_page_and_type(page);
@@ -1289,10 +1288,13 @@ static int put_page_from_l2e(l2_pgentry_
     if ( l2e_get_flags(l2e) & _PAGE_PSE )
     {
         struct page_info *page = l2e_get_page(l2e);
+        bool writeable = l2e_get_flags(l2e) & _PAGE_RW;
         unsigned int i;
 
+        ASSERT(!(mfn_x(page_to_mfn(page)) &
+                 ((1UL << (L2_PAGETABLE_SHIFT - PAGE_SHIFT)) - 1)));
         for ( i = 0; i < (1u << PAGETABLE_ORDER); i++, page++ )
-            put_page_and_type(page);
+            put_data_page(page, writeable);
     }
     else
     {
@@ -1318,7 +1320,7 @@ static int put_page_from_l3e(l3_pgentry_
     if ( unlikely(l3e_get_flags(l3e) & _PAGE_PSE) )
     {
         unsigned long mfn = l3e_get_pfn(l3e);
-        int writeable = l3e_get_flags(l3e) & _PAGE_RW;
+        bool writeable = l3e_get_flags(l3e) & _PAGE_RW;
 
         ASSERT(!(mfn & ((1UL << (L3_PAGETABLE_SHIFT - PAGE_SHIFT)) - 1)));
         do {





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