Commit 67121172 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Allow arbitrary read-only shared pfn-remapping too 



The VM layer (for historical reasons) turns a read-only shared mmap into
a private-like mapping with the VM_MAYWRITE bit clear.  Thus checking
just VM_SHARED isn't actually sufficient.

So use a trivial helper function for the cases where we wanted to inquire
if a mapping was COW-like or not.

Moo!

Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 913f2d79

mm/memory.c

+8 −3
Original line number Diff line number Diff line
@@ -349,6 +349,11 @@ void print_bad_pte(struct vm_area_struct *vma, pte_t pte, unsigned long vaddr) 
	dump_stack();

}



static inline int is_cow_mapping(unsigned int flags)

{

	return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;

}



/*

 * This function gets the "struct page" associated with a pte.

 *
@@ -377,7 +382,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_ 
		unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;

		if (pfn == vma->vm_pgoff + off)

			return NULL;

		if (vma->vm_flags & VM_SHARED)

		if (!is_cow_mapping(vma->vm_flags))

			return NULL;

	}
@@ -439,7 +444,7 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
	 * If it's a COW mapping, write protect it both

	 * in the parent and the child

	 */

	if ((vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE) {

	if (is_cow_mapping(vm_flags)) {

		ptep_set_wrprotect(src_mm, addr, src_pte);

		pte = *src_pte;

	}
@@ -1319,7 +1324,7 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, 
	 * behaviour that some programs depend on. We mark the "original"

	 * un-COW'ed pages by matching them up with "vma->vm_pgoff".

	 */

	if (!(vma->vm_flags & VM_SHARED)) {

	if (is_cow_mapping(vma->vm_flags)) {

		if (addr != vma->vm_start || end != vma->vm_end)

			return -EINVAL;

		vma->vm_pgoff = pfn;

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