x86 mmiotrace: WARN_ONCE if dis/arming a page fails

Print a full warning once, if arming or disarming a page fails.

Also, if initial arming fails, do not handle the page further. This
avoids the possibility of a page failing to arm and then later claiming
to have handled any fault on that page.

WARN_ONCE added by Pekka Paalanen.

Signed-off-by: Stuart Bennett <stuart@freedesktop.org>
Signed-off-by: Pekka Paalanen <pq@iki.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 17 insertions, 8 deletions

diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
index 93d82038af4b..fb1f11546fcd 100644
--- a/arch/x86/mm/kmmio.c
+++ b/arch/x86/mm/kmmio.c
@@ -105,7 +105,7 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
         return NULL;
 }
 
-static void set_page_present(unsigned long addr, bool present,
+static int set_page_present(unsigned long addr, bool present,
                                                         unsigned int *pglevel)
 {
         pteval_t pteval;
@@ -116,7 +116,7 @@ static void set_page_present(unsigned long addr, bool present,
 
         if (!pte) {
                 pr_err("kmmio: no pte for page 0x%08lx\n", addr);
-                return;
+                return -1;
         }
 
         if (pglevel)
@@ -140,22 +140,27 @@ static void set_page_present(unsigned long addr, bool present,
 
         default:
                 pr_err("kmmio: unexpected page level 0x%x.\n", level);
-                return;
+                return -1;
         }
 
         __flush_tlb_one(addr);
+
+        return 0;
 }
 
 /** Mark the given page as not present. Access to it will trigger a fault. */
-static void arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
+static int arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
 {
-        set_page_present(page & PAGE_MASK, false, pglevel);
+        int ret = set_page_present(page & PAGE_MASK, false, pglevel);
+        WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", page);
+        return ret;
 }
 
 /** Mark the given page as present. */
 static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
 {
-        set_page_present(page & PAGE_MASK, true, pglevel);
+        int ret = set_page_present(page & PAGE_MASK, true, pglevel);
+        WARN_ONCE(ret < 0, KERN_ERR "kmmio disarming 0x%08lx failed.\n", page);
 }
 
 /*
@@ -326,9 +331,13 @@ static int add_kmmio_fault_page(unsigned long page)
 
         f->count = 1;
         f->page = page;
-        list_add_rcu(&f->list, kmmio_page_list(f->page));
 
-        arm_kmmio_fault_page(f->page, NULL);
+        if (arm_kmmio_fault_page(f->page, NULL)) {
+                kfree(f);
+                return -1;
+        }
+
+        list_add_rcu(&f->list, kmmio_page_list(f->page));
 
         return 0;
 }