x86/mm/cpa: Make cpa_data::numpages invariant

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom.StDenis@amd.com
Cc: dave.hansen@intel.com
Link: http://lkml.kernel.org/r/20181203171043.493000228@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 351874259a71..12b69263e501 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1625,14 +1625,15 @@ static int cpa_process_alias(struct cpa_data *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;
@@ -1643,12 +1644,12 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
                 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;
                 }
 
                 /*
@@ -1656,11 +1657,15 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
                  * 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;
 }
 
 /*