Re: [Qemu-devel] Re: [PATCH] Make page_find() return 0 for too-large addresses

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Sep 12, 2008 at 05:14:06PM -0300, Eduardo Habkost wrote:
> On Fri, Sep 12, 2008 at 02:50:33PM -0500, Anthony Liguori wrote:
> > Eduardo Habkost wrote:
> >> On some cases, such as under KVM, tb_invalidate_phys_page_range()
> >> may be called for large addresses, when qemu is configured to more than
> >> 4GB of RAM.
> >>
> >> On these cases, qemu was crashing because it was using an index too
> >> large for l1_map[], that supports only 32-bit addresses when compiling
> >> without CONFIG_USER_ONLY.
> >>   
<snip>
> 
> BTW, I've just noticed page_find_alloc() has this:
> 
> #if TARGET_LONG_BITS > 32
>     /* Host memory outside guest VM.  For 32-bit targets we have already
>        excluded high addresses.  */
>     if (index > ((target_ulong)L2_SIZE * L1_SIZE))
>         return NULL;
> #endif
> 
> So, we can just use a similar check on page_find().

New patch, reusing the range check from page_find_alloc() on
page_find(). Untested.


Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
Index: qemu/exec.c
===================================================================
--- qemu/exec.c	(revisão 5200)
+++ qemu/exec.c	(cópia de trabalho)
@@ -279,17 +279,24 @@ static void page_init(void)
 #endif
 }
 
-static inline PageDesc *page_find_alloc(target_ulong index)
+static inline PageDesc **page_l1_map(target_ulong index)
 {
-    PageDesc **lp, *p;
-
 #if TARGET_LONG_BITS > 32
     /* Host memory outside guest VM.  For 32-bit targets we have already
        excluded high addresses.  */
     if (index > ((target_ulong)L2_SIZE * L1_SIZE))
         return NULL;
 #endif
-    lp = &l1_map[index >> L2_BITS];
+    return &l1_map[index >> L2_BITS];
+}
+
+static inline PageDesc *page_find_alloc(target_ulong index)
+{
+    PageDesc **lp, *p;
+    lp = page_l1_map(index);
+    if (!lp)
+        return NULL;
+
     p = *lp;
     if (!p) {
         /* allocate if not found */
@@ -316,9 +323,12 @@ static inline PageDesc *page_find_alloc(
 
 static inline PageDesc *page_find(target_ulong index)
 {
-    PageDesc *p;
+    PageDesc **lp, *p;
+    lp = page_l1_map(index);
+    if (!lp)
+        return NULL;
 
-    p = l1_map[index >> L2_BITS];
+    p = *lp;
     if (!p)
         return 0;
     return p + (index & (L2_SIZE - 1));


-- 
Eduardo