linux-user: Fix h2g usage in page_find_alloc

Paul's comment on my first approach to fix the h2g usage in
page_find_alloc finally open my eyes about what the code is actually
supposed to do:

With the help of h2g_valid we can no cleanly check if a freshly allocate
page (for host usage) is guest-reachable and, in case it is, mark it
reserved in the guest's address range.
Signed-off-by: NJan Kiszka <jan.kiszka@web.de>
Signed-off-by: NKirill A. Shutemov <kirill@shutemov.name>
Acked-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5957 c046a42c-6fe2-441c-8c8c-71466251a162

exec.c

@@ -305,14 +305,13 @@ static inline PageDesc *page_find_alloc(target_ulong index)
     if (!p) {
         /* allocate if not found */
 #if defined(CONFIG_USER_ONLY)
-        unsigned long addr;
         size_t len = sizeof(PageDesc) * L2_SIZE;
         /* Don't use qemu_malloc because it may recurse.  */
         p = mmap(0, len, PROT_READ | PROT_WRITE,
                  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
         *lp = p;
-        addr = h2g(p);
-        if (addr == (target_ulong)addr) {
+        if (h2g_valid(p)) {
+            unsigned long addr = h2g(p);
             page_set_flags(addr & TARGET_PAGE_MASK,
                            TARGET_PAGE_ALIGN(addr + len),
                            PAGE_RESERVED);