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;