tracing: x86, mmiotrace: refactor clearing/restore of page presence

* change function names to clear_* from set_*: in reality we only clear
  and restore page presence, and never unconditionally set present.
  Using clear_*({true, false}, ...) is therefore more honest than
  set_*({false, true}, ...)

* upgrade presence storage to pteval_t: doing user-space tracing will
  require saving and manipulation of the _PAGE_PROTNONE bit, in addition
  to the existing _PAGE_PRESENT changes, and having multiple bools stored
  and passed around does not seem optimal

[ Impact: refactor, clean up mmiotrace code ]

Signed-off-by: Stuart Bennett <stuart@freedesktop.org>
Acked-by: Pekka Paalanen <pq@iki.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1240946271-7083-4-git-send-email-stuart@freedesktop.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 21 deletions

diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
index 869181a917d9..a769d1a2d93b 100644
--- a/arch/x86/mm/kmmio.c
+++ b/arch/x86/mm/kmmio.c
@@ -32,7 +32,7 @@ struct kmmio_fault_page {
         struct list_head list;
         struct kmmio_fault_page *release_next;
         unsigned long page; /* location of the fault page */
-        bool old_presence; /* page presence prior to arming */
+        pteval_t old_presence; /* page presence prior to arming */
         bool armed;
 
         /*
@@ -108,49 +108,51 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
         return NULL;
 }
 
-static void set_pmd_presence(pmd_t *pmd, bool present, bool *old)
+static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
 {
         pmdval_t v = pmd_val(*pmd);
-        *old = !!(v & _PAGE_PRESENT);
-        v &= ~_PAGE_PRESENT;
-        if (present)
-                v |= _PAGE_PRESENT;
+        if (clear) {
+                *old = v & _PAGE_PRESENT;
+                v &= ~_PAGE_PRESENT;
+        } else  /* presume this has been called with clear==true previously */
+                v |= *old;
         set_pmd(pmd, __pmd(v));
 }
 
-static void set_pte_presence(pte_t *pte, bool present, bool *old)
+static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
 {
         pteval_t v = pte_val(*pte);
-        *old = !!(v & _PAGE_PRESENT);
-        v &= ~_PAGE_PRESENT;
-        if (present)
-                v |= _PAGE_PRESENT;
+        if (clear) {
+                *old = v & _PAGE_PRESENT;
+                v &= ~_PAGE_PRESENT;
+        } else  /* presume this has been called with clear==true previously */
+                v |= *old;
         set_pte_atomic(pte, __pte(v));
 }
 
-static int set_page_presence(unsigned long addr, bool present, bool *old)
+static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
 {
         unsigned int level;
-        pte_t *pte = lookup_address(addr, &level);
+        pte_t *pte = lookup_address(f->page, &level);
 
         if (!pte) {
-                pr_err("kmmio: no pte for page 0x%08lx\n", addr);
+                pr_err("kmmio: no pte for page 0x%08lx\n", f->page);
                 return -1;
         }
 
         switch (level) {
         case PG_LEVEL_2M:
-                set_pmd_presence((pmd_t *)pte, present, old);
+                clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
                 break;
         case PG_LEVEL_4K:
-                set_pte_presence(pte, present, old);
+                clear_pte_presence(pte, clear, &f->old_presence);
                 break;
         default:
                 pr_err("kmmio: unexpected page level 0x%x.\n", level);
                 return -1;
         }
 
-        __flush_tlb_one(addr);
+        __flush_tlb_one(f->page);
         return 0;
 }
 
@@ -171,9 +173,9 @@ static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
         WARN_ONCE(f->armed, KERN_ERR "kmmio page already armed.\n");
         if (f->armed) {
                 pr_warning("kmmio double-arm: page 0x%08lx, ref %d, old %d\n",
-                                        f->page, f->count, f->old_presence);
+                                        f->page, f->count, !!f->old_presence);
         }
-        ret = set_page_presence(f->page, false, &f->old_presence);
+        ret = clear_page_presence(f, true);
         WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page);
         f->armed = true;
         return ret;
@@ -182,8 +184,7 @@ static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
 /** Restore the given page to saved presence state. */
 static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
 {
-        bool tmp;
-        int ret = set_page_presence(f->page, f->old_presence, &tmp);
+        int ret = clear_page_presence(f, false);
         WARN_ONCE(ret < 0,
                         KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
         f->armed = false;