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[PATCH v3 03/20] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE

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When handling page fault without holding the mmap_sem the fetch of the
pte lock pointer and the locking will have to be done while ensuring
that the VMA is not touched in our back.

So move the fetch and locking operations in a dedicated function.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
---
 mm/memory.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 13c8c3c8b5e4..530d887ca885 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2408,6 +2408,13 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 }
 
+static bool pte_spinlock(struct vm_fault *vmf)
+{
+	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
+	spin_lock(vmf->ptl);
+	return true;
+}
+
 static bool pte_map_lock(struct vm_fault *vmf)
 {
 	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl);
@@ -3717,8 +3724,8 @@ static int do_numa_page(struct vm_fault *vmf)
 	 * validation through pte_unmap_same(). It's of NUMA type but
 	 * the pfn may be screwed if the read is non atomic.
 	 */
-	vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd);
-	spin_lock(vmf->ptl);
+	if (!pte_spinlock(vmf))
+		return VM_FAULT_RETRY;
 	if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
 		goto out;
@@ -3910,8 +3917,8 @@ static int handle_pte_fault(struct vm_fault *vmf)
 	if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
 		return do_numa_page(vmf);
 
-	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
-	spin_lock(vmf->ptl);
+	if (!pte_spinlock(vmf))
+		return VM_FAULT_RETRY;
 	entry = vmf->orig_pte;
 	if (unlikely(!pte_same(*vmf->pte, entry)))
 		goto unlock;
-- 
2.7.4

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[PATCH v3 00/20] Speculative page faults Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:10 +0200
  [PATCH v3 19/20] x86/mm: Add speculative pagefault handling Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:10 +0200
  [PATCH v3 18/20] perf tools: Add support for the SPF perf event Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:10 +0200
  [PATCH v3 17/20] perf: Add a speculative page fault sw event Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:10 +0200
  [PATCH v3 13/20] mm: Introduce __page_add_new_anon_rmap() Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 10/20] mm: Introduce __lru_cache_add_active_or_unevictable Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 03/20] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 06/20] mm: RCU free VMAs Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 12/20] mm: Introduce __vm_normal_page() Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 05/20] mm: Protect VMA modifications using VMA sequence count Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 01/20] mm: Dont assume page-table invariance during faults Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 09/20] mm/migrate: Pass vm_fault pointer to migrate_misplaced_page() Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200
  [PATCH v3 16/20] mm: Adding speculative page fault failure trace events Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-09-08 20:20 +0200

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