[RFC][PATCH 07/10] x86/mm/cpa: Make cpa_data::numpages invariant

[Peter Zijlstra]

Make sure __change_page_attr_set_clr() doesn't modify cpa->numpages.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
 arch/x86/mm/pageattr.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1623,14 +1623,15 @@ static int cpa_process_alias(struct cpa_
 static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
 {
        unsigned long numpages = cpa->numpages;
-       int ret;
+       unsigned long rempages = numpages;
+       int ret = 0;
 
-       while (numpages) {
+       while (rempages) {
                /*
                 * Store the remaining nr of pages for the large page
                 * preservation check.
                 */
-               cpa->numpages = numpages;
+               cpa->numpages = rempages;
                /* for array changes, we can't use large page */
                if (cpa->flags & (CPA_ARRAY | CPA_PAGES_ARRAY))
                        cpa->numpages = 1;
@@ -1641,12 +1642,12 @@ static int __change_page_attr_set_clr(st
                if (!debug_pagealloc_enabled())
                        spin_unlock(&cpa_lock);
                if (ret)
-                       return ret;
+                       goto out;
 
                if (checkalias) {
                        ret = cpa_process_alias(cpa);
                        if (ret)
-                               return ret;
+                               goto out;
                }
 
                /*
@@ -1654,11 +1655,15 @@ static int __change_page_attr_set_clr(st
                 * CPA operation. Either a large page has been
                 * preserved or a single page update happened.
                 */
-               BUG_ON(cpa->numpages > numpages || !cpa->numpages);
-               numpages -= cpa->numpages;
+               BUG_ON(cpa->numpages > rempages || !cpa->numpages);
+               rempages -= cpa->numpages;
                cpa->curpage += cpa->numpages;
        }
-       return 0;
+
+out:
+       /* Restore the original numpages */
+       cpa->numpages = numpages;
+       return ret;
 }
 
 /*