linux-kernel - [PATCH v4 01/20] mm: Dont assume page-table invariance during faults

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Date:   Mon,  9 Oct 2017 12:07:33 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: [PATCH v4 01/20] mm: Dont assume page-table invariance during faults

From: Peter Zijlstra <peterz@...radead.org>

One of the side effects of speculating on faults (without holding
mmap_sem) is that we can race with free_pgtables() and therefore we
cannot assume the page-tables will stick around.

Remove the reliance on the pte pointer.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

[Remove only if !__HAVE_ARCH_CALL_SPF]
Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
---
 mm/memory.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 6632c9b357c9..4e4fe233d066 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2287,6 +2287,7 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
 }
 EXPORT_SYMBOL_GPL(apply_to_page_range);
 
+#ifndef __HAVE_ARCH_CALL_SPF
 /*
  * handle_pte_fault chooses page fault handler according to an entry which was
  * read non-atomically.  Before making any commitment, on those architectures
@@ -2296,7 +2297,7 @@ EXPORT_SYMBOL_GPL(apply_to_page_range);
  * and do_anonymous_page can safely check later on).
  */
 static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
-				pte_t *page_table, pte_t orig_pte)
+				 pte_t *page_table, pte_t orig_pte)
 {
 	int same = 1;
 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
@@ -2310,6 +2311,7 @@ static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
 	pte_unmap(page_table);
 	return same;
 }
+#endif
 
 static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
 {
@@ -2871,11 +2873,14 @@ int do_swap_page(struct vm_fault *vmf)
 
 	if (vma_readahead)
 		page = swap_readahead_detect(vmf, &swap_ra);
+
+#ifndef __HAVE_ARCH_CALL_SPF
 	if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) {
 		if (page)
 			put_page(page);
 		goto out;
 	}
+#endif
 
 	entry = pte_to_swp_entry(vmf->orig_pte);
 	if (unlikely(non_swap_entry(entry))) {
-- 
2.7.4