x86: delay CPA self-test and repeat it

delay the CPA self-test so that any impact (corruption) of
user-space pagetables can be triggered. Repeat the test
every 30 seconds.

this would have prevented the bug fixed by 8cb2a7c1e95e472b5,
at its source.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 53 insertions, 16 deletions

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 2e1e3af28c3a..fa555148823d 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -220,9 +220,9 @@ config DEBUG_BOOT_PARAMS
           This option will cause struct boot_params to be exported via debugfs.
 
 config CPA_DEBUG
-        bool "CPA self test code"
+        bool "CPA self-test code"
         depends on DEBUG_KERNEL
         help
-          Do change_page_attr self tests at boot.
+          Do change_page_attr() self-tests every 30 seconds.
 
 endmenu
diff --git a/arch/x86/mm/pageattr-test.c b/arch/x86/mm/pageattr-test.c
index 398f3a578dde..ed8201600354 100644
--- a/arch/x86/mm/pageattr-test.c
+++ b/arch/x86/mm/pageattr-test.c
@@ -5,6 +5,7 @@
  * and compares page tables forwards and afterwards.
  */
 #include <linux/bootmem.h>
+#include <linux/kthread.h>
 #include <linux/random.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
@@ -14,8 +15,13 @@
 #include <asm/pgtable.h>
 #include <asm/kdebug.h>
 
+/*
+ * Only print the results of the first pass:
+ */
+static __read_mostly int print = 1;
+
 enum {
-        NTEST                   = 4000,
+        NTEST                   = 400,
 #ifdef CONFIG_X86_64
         LPS                     = (1 << PMD_SHIFT),
 #elif defined(CONFIG_X86_PAE)
@@ -31,7 +37,7 @@ struct split_state {
         long min_exec, max_exec;
 };
 
-static __init int print_split(struct split_state *s)
+static int print_split(struct split_state *s)
 {
         long i, expected, missed = 0;
         int printed = 0;
@@ -82,10 +88,13 @@ static __init int print_split(struct split_state *s)
                                 s->max_exec = addr;
                 }
         }
-        printk(KERN_INFO
-                "CPA mapping 4k %lu large %lu gb %lu x %lu[%lx-%lx] miss %lu\n",
-                s->spg, s->lpg, s->gpg, s->exec,
-                s->min_exec != ~0UL ? s->min_exec : 0, s->max_exec, missed);
+        if (print) {
+                printk(KERN_INFO
+                        " 4k %lu large %lu gb %lu x %lu[%lx-%lx] miss %lu\n",
+                        s->spg, s->lpg, s->gpg, s->exec,
+                        s->min_exec != ~0UL ? s->min_exec : 0,
+                        s->max_exec, missed);
+        }
 
         expected = (s->gpg*GPS + s->lpg*LPS)/PAGE_SIZE + s->spg + missed;
         if (expected != i) {
@@ -96,11 +105,11 @@ static __init int print_split(struct split_state *s)
         return err;
 }
 
-static unsigned long __initdata addr[NTEST];
-static unsigned int __initdata len[NTEST];
+static unsigned long addr[NTEST];
+static unsigned int len[NTEST];
 
 /* Change the global bit on random pages in the direct mapping */
-static __init int exercise_pageattr(void)
+static int pageattr_test(void)
 {
         struct split_state sa, sb, sc;
         unsigned long *bm;
@@ -110,7 +119,8 @@ static __init int exercise_pageattr(void)
         int i, k;
         int err;
 
-        printk(KERN_INFO "CPA exercising pageattr\n");
+        if (print)
+                printk(KERN_INFO "CPA self-test:\n");
 
         bm = vmalloc((max_pfn_mapped + 7) / 8);
         if (!bm) {
@@ -186,7 +196,6 @@ static __init int exercise_pageattr(void)
 
         failed += print_split(&sb);
 
-        printk(KERN_INFO "CPA reverting everything\n");
         for (i = 0; i < NTEST; i++) {
                 if (!addr[i])
                         continue;
@@ -214,12 +223,40 @@ static __init int exercise_pageattr(void)
         failed += print_split(&sc);
 
         if (failed) {
-                printk(KERN_ERR "CPA selftests NOT PASSED. Please report.\n");
+                printk(KERN_ERR "NOT PASSED. Please report.\n");
                 WARN_ON(1);
+                return -EINVAL;
         } else {
-                printk(KERN_INFO "CPA selftests PASSED\n");
+                if (print)
+                        printk(KERN_INFO "ok.\n");
         }
 
         return 0;
 }
-module_init(exercise_pageattr);
+
+static int do_pageattr_test(void *__unused)
+{
+        while (!kthread_should_stop()) {
+                schedule_timeout_interruptible(HZ*30);
+                if (pageattr_test() < 0)
+                        break;
+                if (print)
+                        print--;
+        }
+        return 0;
+}
+
+static int start_pageattr_test(void)
+{
+        struct task_struct *p;
+
+        p = kthread_create(do_pageattr_test, NULL, "pageattr-test");
+        if (!IS_ERR(p))
+                wake_up_process(p);
+        else
+                WARN_ON(1);
+
+        return 0;
+}
+
+module_init(start_pageattr_test);