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From: Alan Cox <alc@FreeBSD.org>
Date: Sat, 10 Dec 2011 18:42:00 +0000 (UTC)
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Subject: svn commit: r228398 - head/sys/i386/include
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Author: alc
Date: Sat Dec 10 18:42:00 2011
New Revision: 228398
URL: http://svn.freebsd.org/changeset/base/228398

Log:
  Avoid the possibility of integer overflow in the calculation of
  VM_KMEM_SIZE_MAX.  Specifically, if the user/kernel address space split
  was changed such that the kernel address space was greater than or equal
  to 2 GB, then overflow would occur.
  
  PR:		161721
  MFC after:	3 weeks

Modified:
  head/sys/i386/include/vmparam.h

Modified: head/sys/i386/include/vmparam.h
==============================================================================
--- head/sys/i386/include/vmparam.h	Sat Dec 10 18:35:26 2011	(r228397)
+++ head/sys/i386/include/vmparam.h	Sat Dec 10 18:42:00 2011	(r228398)
@@ -186,11 +186,12 @@
 #endif
 
 /*
- * Ceiling on amount of kmem_map kva space.
+ * Ceiling on the amount of kmem_map KVA space: 40% of the entire KVA space
+ * rounded to the nearest multiple of the superpage size.
  */
 #ifndef VM_KMEM_SIZE_MAX
-#define	VM_KMEM_SIZE_MAX	((VM_MAX_KERNEL_ADDRESS - \
-    VM_MIN_KERNEL_ADDRESS) * 2 / 5)
+#define	VM_KMEM_SIZE_MAX	(((((VM_MAX_KERNEL_ADDRESS - \
+    VM_MIN_KERNEL_ADDRESS) >> (PDRSHIFT - 2)) + 5) / 10) << PDRSHIFT)
 #endif
 
 /* initial pagein size of beginning of executable file */