[PATCH 4/8] mm: introduce do_read_fault()

["Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>]

This patch introduces do_read_fault(). The function does what do_fault()
does for read page faults.

Unlike do_fault(), do_read_fault() is pretty clean and straight-forward.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/memory.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index d3317ac02a5b..cbc17f47df11 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3317,6 +3317,43 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address,
 	return ret;
 }
 
+static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+		unsigned long address, pmd_t *pmd,
+		pgoff_t pgoff, unsigned int flags, pte_t orig_pte)
+{
+	struct page *fault_page;
+	spinlock_t *ptl;
+	pte_t entry, *pte;
+	int ret;
+
+	ret = __do_fault(vma, address, pgoff, flags, &fault_page);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		return ret;
+
+	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
+	if (unlikely(!pte_same(*pte, orig_pte))) {
+		pte_unmap_unlock(pte, ptl);
+		unlock_page(fault_page);
+		page_cache_release(fault_page);
+		return ret;
+	}
+
+	flush_icache_page(vma, fault_page);
+	entry = mk_pte(fault_page, vma->vm_page_prot);
+	if (pte_file(orig_pte) && pte_file_soft_dirty(orig_pte))
+		pte_mksoft_dirty(entry);
+	inc_mm_counter_fast(mm, MM_FILEPAGES);
+	page_add_file_rmap(fault_page);
+	set_pte_at(mm, address, pte, entry);
+
+	/* no need to invalidate: a not-present page won't be cached */
+	update_mmu_cache(vma, address, pte);
+	pte_unmap_unlock(pte, ptl);
+	unlock_page(fault_page);
+
+	return ret;
+}
+
 /*
  * do_fault() tries to create a new page mapping. It aggressively
  * tries to share with existing pages, but makes a separate copy if
@@ -3510,6 +3547,9 @@ static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 			- vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 
 	pte_unmap(page_table);
+	if (!(flags & FAULT_FLAG_WRITE))
+		return do_read_fault(mm, vma, address, pmd, pgoff, flags,
+				orig_pte);
 	return do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
 }
 
@@ -3542,6 +3582,9 @@ static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	}
 
 	pgoff = pte_to_pgoff(orig_pte);
+	if (!(flags & FAULT_FLAG_WRITE))
+		return do_read_fault(mm, vma, address, pmd, pgoff, flags,
+				orig_pte);
 	return do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
 }
 
-- 
1.8.5.4

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