[Xen-devel] [PATCH] fix off-by-one mistakes in vm_alloc()

["Jan Beulich" <JBeulich@xxxxxxxx>]

Also add another pair of assertions to catch eventual further cases of
incorrect accounting, and remove the temporary debuggin messages again
which commit 68caac7f ("x86: don't use destroy_xen_mappings() for
vunmap()") added.

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

--- a/xen/common/vmap.c
+++ b/xen/common/vmap.c
@@ -57,8 +57,8 @@ void *vm_alloc(unsigned int nr, unsigned
     {
         struct page_info *pg;
 
-        ASSERT(!test_bit(vm_low, vm_bitmap));
-        for ( start = vm_low; ; )
+        ASSERT(vm_low == vm_top || !test_bit(vm_low, vm_bitmap));
+        for ( start = vm_low; start < vm_top; )
         {
             bit = find_next_bit(vm_bitmap, vm_top, start + 1);
             if ( bit > vm_top )
@@ -68,12 +68,18 @@ void *vm_alloc(unsigned int nr, unsigned
              * corresponding page a guard one.
              */
             start = (start + align) & ~(align - 1);
-            if ( start + nr <= bit )
-                break;
-            start = bit < vm_top ?
-                    find_next_zero_bit(vm_bitmap, vm_top, bit + 1) : bit;
-            if ( start >= vm_top )
-                break;
+            if ( bit < vm_top )
+            {
+                if ( start + nr < bit )
+                    break;
+                start = find_next_zero_bit(vm_bitmap, vm_top, bit + 1);
+            }
+            else
+            {
+                if ( start + nr <= bit )
+                    break;
+                start = bit;
+            }
         }
 
         if ( start < vm_top )
@@ -115,6 +121,10 @@ void *vm_alloc(unsigned int nr, unsigned
 
     for ( bit = start; bit < start + nr; ++bit )
         __set_bit(bit, vm_bitmap);
+    if ( bit < vm_top )
+        ASSERT(!test_bit(bit, vm_bitmap));
+    else
+        ASSERT(bit == vm_top);
     if ( start <= vm_low + 2 )
         vm_low = bit;
     spin_unlock(&vm_lock);
@@ -177,7 +187,6 @@ void *__vmap(const unsigned long *mfn, u
     void *va = vm_alloc(nr * granularity, align);
     unsigned long cur = (unsigned long)va;
 
-printk("vmap(%p:%#x)\n", va, nr * granularity);//temp
     for ( ; va && nr--; ++mfn, cur += PAGE_SIZE * granularity )
     {
         if ( map_pages_to_xen(cur, *mfn, granularity, flags) )
@@ -202,7 +211,6 @@ void vunmap(const void *va)
 
     destroy_xen_mappings(addr, addr + PAGE_SIZE * vm_size(va));
 #else /* Avoid tearing down intermediate page tables. */
-printk("vunmap(%p:%#x)\n", va, vm_size(va));//temp
     map_pages_to_xen((unsigned long)va, 0, vm_size(va), _PAGE_NONE);
 #endif
     vm_free(va);

Attachment: vmap-off-by-one.patch
Description: Text document

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