linux-kernel - [PATCH] Inconsistent mmap()/mremap() flags

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Date:	Thu, 27 Sep 2007 23:46:33 -0600
From:	Thayne Harbaugh <thayne@...net>
To:	linux-kernel@...r.kernel.org
Cc:	ak@...e.de, linux-mm@...ck.org, discuss@...-64.org
Subject: [PATCH] Inconsistent mmap()/mremap() flags

The x86_64 mmap() accepts the MAP_32BIT flag to request 32-bit clean
addresses.  It seems to me that for consistency x86_64 mremap() should
also accept this (or an equivalent) flag.

Here is a trivial and untested patch for basis of discussion:

--- linux-source-2.6.22/mm/mremap.c.orig	2007-09-27 23:02:13.000000000 -0600
+++ linux-source-2.6.22/mm/mremap.c	2007-09-27 23:07:29.000000000 -0600
@@ -23,6 +23,11 @@
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>

+/* MAP_32BIT possibly defined in asm/mman.h */
+#ifndef MAP_32BIT
+#define MAP_32BIT 0
+#endif
+
 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 {
 	pgd_t *pgd;
@@ -255,7 +259,7 @@
 	unsigned long ret = -EINVAL;
 	unsigned long charged = 0;
 
-	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
+	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MAP_32BIT))
 		goto out;
 
 	if (addr & ~PAGE_MASK)
@@ -388,6 +392,9 @@
 			if (vma->vm_flags & VM_MAYSHARE)
 				map_flags |= MAP_SHARED;
 
+			if (flags & MAP_32BIT)
+				map_flags |= MAP_32BIT;
+
 			new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 						vma->vm_pgoff, map_flags);
 			ret = new_addr;


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