[RFC][PATCH 1/5] rmap: add new exported function: page_wrprotect()

[Izik Eidus <izike-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

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>From 45e5a255b004e0d578007576304a6b1e272fcb67 Mon Sep 17 00:00:00 2001
From: Izik Eidus <izike-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
Date: Mon, 21 Jan 2008 16:59:35 +0200
Subject: [PATCH] rmap: add new exported function: page_wrprotect(),
 page_wrprotect() make the page as read only by setting the ptes point to
 it as read only.

Signed-off-by: Izik Eidus <izike-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
---
 include/linux/rmap.h |    7 ++++
 mm/rmap.c            |   91 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+), 0 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 97347f2..dac41af 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -108,6 +108,8 @@ unsigned long page_address_in_vma(struct page *, struct vm_area_struct *);
  */
 int page_mkclean(struct page *);
 
+int page_wrprotect(struct page *page);
+
 #else	/* !CONFIG_MMU */
 
 #define anon_vma_init()		do {} while (0)
@@ -122,6 +124,11 @@ static inline int page_mkclean(struct page *page)
 	return 0;
 }
 
+static inline int page_wrprotect(struct page *page)
+{
+	return 0;
+}
+
 
 #endif	/* CONFIG_MMU */
 
diff --git a/mm/rmap.c b/mm/rmap.c
index dbc2ca2..462b7c9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -484,6 +484,97 @@ int page_mkclean(struct page *page)
 }
 EXPORT_SYMBOL_GPL(page_mkclean);
 
+static int page_wrprotect_one(struct page *page, struct vm_area_struct *vma)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long address;
+	pte_t *pte;
+	spinlock_t *ptl;
+	int ret = 0;
+
+	address = vma_address(page, vma);
+	if (address == -EFAULT)
+		goto out;
+
+	pte = page_check_address(page, mm, address, &ptl);
+	if (!pte)
+		goto out;
+
+	if (pte_write(*pte)) {
+		pte_t entry;
+
+		flush_cache_page(vma, address, pte_pfn(*pte));
+		entry = ptep_clear_flush(vma, address, pte);
+		entry = pte_wrprotect(entry);
+		set_pte_at(mm, address, pte, entry);
+	}
+	ret = 1;
+
+	pte_unmap_unlock(pte, ptl);
+out:
+	return ret;
+}
+
+static int page_wrprotect_file(struct page *page)
+{
+	struct address_space *mapping;
+	struct prio_tree_iter iter;
+	struct vm_area_struct *vma;
+	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+	int ret = 0;
+
+	mapping = page_mapping(page);
+	if (!mapping)
+		return ret;
+
+	spin_lock(&mapping->i_mmap_lock);
+
+	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff)
+		ret += page_wrprotect_one(page, vma);
+
+	spin_unlock(&mapping->i_mmap_lock);
+
+	return ret;
+}
+
+static int page_wrprotect_anon(struct page *page)
+{
+	struct vm_area_struct *vma;
+	struct anon_vma *anon_vma;
+	int ret = 0;
+
+	anon_vma = page_lock_anon_vma(page);
+	if (!anon_vma)
+		return ret;
+
+	list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
+		ret += page_wrprotect_one(page, vma);
+
+	page_unlock_anon_vma(anon_vma);
+
+	return ret;
+}
+
+/**
+ * set all the ptes pointed to a page as read only
+ * return the number of ptes that were set as read only
+ * (ptes that were read only before this was called are counted as well)
+ */
+int page_wrprotect(struct page *page)
+{
+	int ret = 0;
+
+	BUG_ON(!PageLocked(page));
+
+	if (PageAnon(page))
+		ret = page_wrprotect_anon(page);
+	else
+		ret = page_wrprotect_file(page);
+
+	return ret;
+}
+EXPORT_SYMBOL(page_wrprotect);
+
 /**
  * page_set_anon_rmap - setup new anonymous rmap
  * @page:	the page to add the mapping to
-- 
1.5.3.6


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