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Commit f33ea7f4 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[PATCH] fix get_user_pages bug 



Checking pte_dirty instead of pte_write in __follow_page is problematic
for s390, and for copy_one_pte which leaves dirty when clearing write.

So revert __follow_page to check pte_write as before, and make
do_wp_page pass back a special extra VM_FAULT_WRITE bit to say it has
done its full job: once get_user_pages receives this value, it no longer
requires pte_write in __follow_page.

But most callers of handle_mm_fault, in the various architectures, have
switch statements which do not expect this new case.  To avoid changing
them all in a hurry, make an inline wrapper function (using the old
name) that masks off the new bit, and use the extended interface with
double underscores.

Yes, we do have a call to do_wp_page from do_swap_page, but no need to
change that: in rare case it's needed, another do_wp_page will follow.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
[ Cleanups by Nick Piggin ]
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5cb4cc0d

include/linux/mm.h

+17 −5
Original line number Diff line number Diff line
@@ -625,10 +625,16 @@ static inline int page_mapped(struct page *page) 
 * Used to decide whether a process gets delivered SIGBUS or

 * just gets major/minor fault counters bumped up.

 */

#define VM_FAULT_OOM	(-1)

#define VM_FAULT_SIGBUS	0

#define VM_FAULT_MINOR	1

#define VM_FAULT_MAJOR	2

#define VM_FAULT_OOM	0x00

#define VM_FAULT_SIGBUS	0x01

#define VM_FAULT_MINOR	0x02

#define VM_FAULT_MAJOR	0x03



/* 

 * Special case for get_user_pages.

 * Must be in a distinct bit from the above VM_FAULT_ flags.

 */

#define VM_FAULT_WRITE	0x10



#define offset_in_page(p)	((unsigned long)(p) & ~PAGE_MASK)
@@ -704,7 +710,13 @@ extern pte_t *FASTCALL(pte_alloc_kernel(struct mm_struct *mm, pmd_t *pmd, unsign 
extern pte_t *FASTCALL(pte_alloc_map(struct mm_struct *mm, pmd_t *pmd, unsigned long address));

extern int install_page(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, struct page *page, pgprot_t prot);

extern int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, unsigned long pgoff, pgprot_t prot);

extern int handle_mm_fault(struct mm_struct *mm,struct vm_area_struct *vma, unsigned long address, int write_access);

extern int __handle_mm_fault(struct mm_struct *mm,struct vm_area_struct *vma, unsigned long address, int write_access);



static inline int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access)

{

	return __handle_mm_fault(mm, vma, address, write_access) & (~VM_FAULT_WRITE);

}



extern int make_pages_present(unsigned long addr, unsigned long end);

extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write);

void install_arg_page(struct vm_area_struct *, struct page *, unsigned long);

mm/memory.c

+23 −8
Original line number Diff line number Diff line
@@ -811,15 +811,18 @@ static struct page *__follow_page(struct mm_struct *mm, unsigned long address, 
	pte = *ptep;

	pte_unmap(ptep);

	if (pte_present(pte)) {

		if (write && !pte_dirty(pte))

		if (write && !pte_write(pte))

			goto out;

		if (read && !pte_read(pte))

			goto out;

		pfn = pte_pfn(pte);

		if (pfn_valid(pfn)) {

			page = pfn_to_page(pfn);

			if (accessed)

			if (accessed) {

				if (write && !pte_dirty(pte) &&!PageDirty(page))

					set_page_dirty(page);

				mark_page_accessed(page);

			}

			return page;

		}

	}
@@ -941,10 +944,11 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
		}

		spin_lock(&mm->page_table_lock);

		do {

			int write_access = write;

			struct page *page;



			cond_resched_lock(&mm->page_table_lock);

			while (!(page = follow_page(mm, start, write))) {

			while (!(page = follow_page(mm, start, write_access))) {

				/*

				 * Shortcut for anonymous pages. We don't want

				 * to force the creation of pages tables for
@@ -957,7 +961,16 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
					break;

				}

				spin_unlock(&mm->page_table_lock);

				switch (handle_mm_fault(mm,vma,start,write)) {

				switch (__handle_mm_fault(mm, vma, start,

							write_access)) {

				case VM_FAULT_WRITE:

					/*

					 * do_wp_page has broken COW when

					 * necessary, even if maybe_mkwrite

					 * decided not to set pte_write

					 */

					write_access = 0;

					/* FALLTHRU */

				case VM_FAULT_MINOR:

					tsk->min_flt++;

					break;
@@ -1220,6 +1233,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma, 
	struct page *old_page, *new_page;

	unsigned long pfn = pte_pfn(pte);

	pte_t entry;

	int ret;



	if (unlikely(!pfn_valid(pfn))) {

		/*
@@ -1247,7 +1261,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma, 
			lazy_mmu_prot_update(entry);

			pte_unmap(page_table);

			spin_unlock(&mm->page_table_lock);

			return VM_FAULT_MINOR;

			return VM_FAULT_MINOR|VM_FAULT_WRITE;

		}

	}

	pte_unmap(page_table);
@@ -1274,6 +1288,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma, 
	/*

	 * Re-check the pte - we dropped the lock

	 */

	ret = VM_FAULT_MINOR;

	spin_lock(&mm->page_table_lock);

	page_table = pte_offset_map(pmd, address);

	if (likely(pte_same(*page_table, pte))) {
@@ -1290,12 +1305,13 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma, 


		/* Free the old page.. */

		new_page = old_page;

		ret |= VM_FAULT_WRITE;

	}

	pte_unmap(page_table);

	page_cache_release(new_page);

	page_cache_release(old_page);

	spin_unlock(&mm->page_table_lock);

	return VM_FAULT_MINOR;

	return ret;



no_new_page:

	page_cache_release(old_page);
@@ -1987,7 +2003,6 @@ static inline int handle_pte_fault(struct mm_struct *mm, 
	if (write_access) {

		if (!pte_write(entry))

			return do_wp_page(mm, vma, address, pte, pmd, entry);



		entry = pte_mkdirty(entry);

	}

	entry = pte_mkyoung(entry);
@@ -2002,7 +2017,7 @@ static inline int handle_pte_fault(struct mm_struct *mm, 
/*

 * By the time we get here, we already hold the mm semaphore

 */

int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,

int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,

		unsigned long address, int write_access)

{

	pgd_t *pgd;