Commit b51ad4f8 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/memory: slightly simplify copy_present_pte() 

Let's move the pinning check into the caller, to simplify return code
logic and prepare for further changes: relocating the
page_needs_cow_for_dma() into rmap handling code.

While at it, remove the unused pte parameter and simplify the comments a
bit.

No functional change intended.

Link: https://lkml.kernel.org/r/20220428083441.37290-4-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 623a1ddf

mm/memory.c

+16 −37
Original line number Diff line number Diff line
@@ -862,19 +862,11 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
}



/*

 * Copy a present and normal page if necessary.

 * Copy a present and normal page.

 *

 * NOTE! The usual case is that this doesn't need to do

 * anything, and can just return a positive value. That

 * will let the caller know that it can just increase

 * the page refcount and re-use the pte the traditional

 * way.

 *

 * But _if_ we need to copy it because it needs to be

 * pinned in the parent (and the child should get its own

 * copy rather than just a reference to the same page),

 * we'll do that here and return zero to let the caller

 * know we're done.

 * NOTE! The usual case is that this isn't required;

 * instead, the caller can just increase the page refcount

 * and re-use the pte the traditional way.

 *

 * And if we need a pre-allocated page but don't yet have

 * one, return a negative error to let the preallocation
@@ -884,25 +876,10 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
static inline int

copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,

		  pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,

		  struct page **prealloc, pte_t pte, struct page *page)

		  struct page **prealloc, struct page *page)

{

	struct page *new_page;



	/*

	 * What we want to do is to check whether this page may

	 * have been pinned by the parent process.  If so,

	 * instead of wrprotect the pte on both sides, we copy

	 * the page immediately so that we'll always guarantee

	 * the pinned page won't be randomly replaced in the

	 * future.

	 *

	 * The page pinning checks are just "has this mm ever

	 * seen pinning", along with the (inexact) check of

	 * the page count. That might give false positives for

	 * for pinning, but it will work correctly.

	 */

	if (likely(!page_needs_cow_for_dma(src_vma, page)))

		return 1;

	pte_t pte;



	new_page = *prealloc;

	if (!new_page)
@@ -944,14 +921,16 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, 
	struct page *page;



	page = vm_normal_page(src_vma, addr, pte);

	if (page) {

		int retval;



		retval = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,

					   addr, rss, prealloc, pte, page);

		if (retval <= 0)

			return retval;



	if (page && unlikely(page_needs_cow_for_dma(src_vma, page))) {

		/*

		 * If this page may have been pinned by the parent process,

		 * copy the page immediately for the child so that we'll always

		 * guarantee the pinned page won't be randomly replaced in the

		 * future.

		 */

		return copy_present_page(dst_vma, src_vma, dst_pte, src_pte,

					 addr, rss, prealloc, page);

	} else if (page) {

		get_page(page);

		page_dup_rmap(page, false);

		rss[mm_counter(page)]++;