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

Peter Zijlstra
2018-12-03T17:14:33Z

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@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;
}

/*