uml: deal with inaccessible address space start

This patch makes os_get_task_size locate the bottom of the address space,
as well as the top.  This is for systems which put a lower limit on mmap
addresses.  It works by manually scanning pages from zero onwards until a
valid page is found.

Because the bottom of the address space may not be zero, it's not
sufficient to assume the top of the address space is the size of the
address space.  The size is the difference between the top address and
bottom address.

[jdike@addtoit.com: changed the name to reflect that this function is
supposed to return the top of the process address space, not its size and
changed the return value to reflect that.  Also some minor formatting
changes]
Signed-off-by: Tom Spink <tspink@gmail.com>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index e2716ac8889accd7f33ca8d381f014d3b1bd7283..db5be46e3e186677c8f16c93f585e82413d7740f 100644 (file)
--- 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 9db85b2ce6987141f314ea0dcc8ddc7f8960cdeb..8d84250324b3d2c41d2a6718e7fd0531ecd025b4 100644 (file)
--- 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 ccb49b0aff598d673659d12a8e7249feb485fdee..be04c1e183bfec5d3ccafb26bc4456c5f901c9d6 100644 (file)
--- 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 fad6f57f8ee3568d89ae8603238d5c734e19cb3a..26a0dd1f349c62600e8415e81c59a807e054a9d5 100644 (file)
--- 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;