Not correctly setup reverse mapping in move_page_range

[noobmyq]

When moving pages to the new process in phx_restart, the reverse mapping is not correctly setup, resulting in the fields anon_vma in vm_area_struct is a null pointer.

vma->anon_vma == NULL

And in the move_page_range function, this would cause an early return in line 1508:

phoenix-kernel/mm/memory.c

Lines 1489 to 1508 in b4e8179

	move_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
	{
	pgd_t *src_pgd, *dst_pgd;
	unsigned long next;
	unsigned long addr = src_vma->vm_start;
	unsigned long end = src_vma->vm_end;
	struct mm_struct *dst_mm = dst_vma->vm_mm;
	struct mm_struct *src_mm = src_vma->vm_mm;
	struct mmu_notifier_range range;
	int ret;
	/*
	* Don't copy ptes where a page fault will fill them correctly.
	* Fork becomes much lighter when there are big shared or private
	* readonly mappings. The tradeoff is that copy_page_range is more
	* efficient than faulting.
	*/
	if (!(src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) &&
	!src_vma->anon_vma)
	return 0;

Current temporary make-up solution is calling anon_vma_fork after moving pages:

phoenix-kernel/mm/memory.c

Lines 1562 to 1581 in 1e76d17

	ret = 0;
	dst_pgd = pgd_offset(dst_mm, addr);
	src_pgd = pgd_offset(src_mm, addr);
	do {
	next = pgd_addr_end(addr, end);
	if (pgd_none_or_clear_bad(src_pgd))
	continue;
	if (unlikely(move_p4d_range(dst_vma, src_vma, dst_pgd, src_pgd,
	addr, next))) {
	ret = -ENOMEM;
	break;
	}
	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
	/* TODO: add the following line may help multiple recoveries? */
	if (anon_vma_fork(dst_vma, src_vma)) {
	printk("anon_vma_fork failed, but why?");
	ret = -ENOMEM;
	}

Which may results in additional cost to the memory since we don't need all the reverse mapping that a fork system call needs.