mm: add zap_vma_ptes(): a library function to unmap driver ptes

struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,

		pte_t pte);

int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,

		unsigned long size);

unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,

		unsigned long size, struct zap_details *);

unsigned long unmap_vmas(struct mmu_gather **tlb,

	return end;

}

/**

 * zap_vma_ptes - remove ptes mapping the vma

 * @vma: vm_area_struct holding ptes to be zapped

 * @address: starting address of pages to zap

 * @size: number of bytes to zap

 *

 * This function only unmaps ptes assigned to VM_PFNMAP vmas.

 *

 * The entire address range must be fully contained within the vma.

 *

 * Returns 0 if successful.

 */

int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,

		unsigned long size)

{

	if (address < vma->vm_start || address + size > vma->vm_end ||

	    		!(vma->vm_flags & VM_PFNMAP))

		return -1;

	zap_page_range(vma, address, size, NULL);

	return 0;

}

EXPORT_SYMBOL_GPL(zap_vma_ptes);

/*

 * Do a quick page-table lookup for a single page.

 */