4 files changed, 26 insertions, 11 deletions

diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index e2716ac8889a..db5be46e3e18 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -299,6 +299,6 @@ extern int os_arch_prctl(int pid, int code, unsigned long *addr);
 extern int get_pty(void);
 
 /* sys-$ARCH/task_size.c */
-extern unsigned long os_get_task_size(void);
+extern unsigned long os_get_top_address(void);
 
 #endif
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 9db85b2ce698..8d84250324b3 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -274,7 +274,7 @@ int __init linux_main(int argc, char **argv)
         if (have_root == 0)
                 add_arg(DEFAULT_COMMAND_LINE);
 
-        host_task_size = os_get_task_size();
+        host_task_size = os_get_top_address();
         /*
          * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
          * out
diff --git a/arch/um/os-Linux/sys-i386/task_size.c b/arch/um/os-Linux/sys-i386/task_size.c
index ccb49b0aff59..be04c1e183bf 100644
--- a/arch/um/os-Linux/sys-i386/task_size.c
+++ b/arch/um/os-Linux/sys-i386/task_size.c
@@ -63,7 +63,7 @@ static int page_ok(unsigned long page)
         return ok;
 }
 
-unsigned long os_get_task_size(void)
+unsigned long os_get_top_address(void)
 {
         struct sigaction sa, old;
         unsigned long bottom = 0;
@@ -76,9 +76,9 @@ unsigned long os_get_task_size(void)
          * hosts, but shouldn't hurt otherwise.
          */
         unsigned long top = 0xffffd000 >> UM_KERN_PAGE_SHIFT;
-        unsigned long test;
+        unsigned long test, original;
 
-        printf("Locating the top of the address space ... ");
+        printf("Locating the bottom of the address space ... ");
         fflush(stdout);
 
         /*
@@ -89,16 +89,31 @@ unsigned long os_get_task_size(void)
         sigemptyset(&sa.sa_mask);
         sa.sa_flags = SA_NODEFER;
         if (sigaction(SIGSEGV, &sa, &old)) {
-                perror("os_get_task_size");
+                perror("os_get_top_address");
                 exit(1);
         }
 
-        if (!page_ok(bottom)) {
-                fprintf(stderr, "Address 0x%x no good?\n",
-                        bottom << UM_KERN_PAGE_SHIFT);
+        /* Manually scan the address space, bottom-up, until we find
+         * the first valid page (or run out of them).
+         */
+        for (bottom = 0; bottom < top; bottom++) {
+                if (page_ok(bottom))
+                        break;
+        }
+
+        /* If we've got this far, we ran out of pages. */
+        if (bottom == top) {
+                fprintf(stderr, "Unable to determine bottom of address "
+                        "space.\n");
                 exit(1);
         }
 
+        printf("0x%x\n", bottom << UM_KERN_PAGE_SHIFT);
+        printf("Locating the top of the address space ... ");
+        fflush(stdout);
+
+        original = bottom;
+
         /* This could happen with a 4G/4G split */
         if (page_ok(top))
                 goto out;
@@ -114,7 +129,7 @@ unsigned long os_get_task_size(void)
 out:
         /* Restore the old SIGSEGV handling */
         if (sigaction(SIGSEGV, &old, NULL)) {
-                perror("os_get_task_size");
+                perror("os_get_top_address");
                 exit(1);
         }
         top <<= UM_KERN_PAGE_SHIFT;
diff --git a/arch/um/os-Linux/sys-x86_64/task_size.c b/arch/um/os-Linux/sys-x86_64/task_size.c
index fad6f57f8ee3..26a0dd1f349c 100644
--- a/arch/um/os-Linux/sys-x86_64/task_size.c
+++ b/arch/um/os-Linux/sys-x86_64/task_size.c
@@ -1,4 +1,4 @@
-unsigned long os_get_task_size(unsigned long shift)
+unsigned long os_get_top_address(unsigned long shift)
 {
         /* The old value of CONFIG_TOP_ADDR */
         return 0x7fc0000000;