Commit 4eae4efa authored by Peter Xu's avatar Peter Xu Committed by Linus Torvalds
Browse files

hugetlb: do early cow when page pinned on src mm 

This is the last missing piece of the COW-during-fork effort when there're
pinned pages found.  One can reference 70e806e4 ("mm: Do early cow for
pinned pages during fork() for ptes", 2020-09-27) for more information,
since we do similar things here rather than pte this time, but just for
hugetlb.

Note that after Jason's recent work on 57efa1fe ("mm/gup: prevent
gup_fast from racing with COW during fork", 2020-12-15) which is safer and
easier to understand, we're safe now within the whole copy_page_range()
against gup-fast, we don't need the wr-protect trick that proposed in
70e806e4 anymore.

Link: https://lkml.kernel.org/r/20210217233547.93892-6-peterx@redhat.com


Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@ziepe.ca>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Gal Pressman <galpress@amazon.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Kirill Shutemov <kirill@shutemov.name>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Roland Scheidegger <sroland@vmware.com>
Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Wei Zhang <wzam@amazon.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ca6eb14d

mm/hugetlb.c

+62 −4
Original line number Diff line number Diff line
@@ -3728,6 +3728,18 @@ static bool is_hugetlb_entry_hwpoisoned(pte_t pte) 
		return false;

}



static void

hugetlb_install_page(struct vm_area_struct *vma, pte_t *ptep, unsigned long addr,

		     struct page *new_page)

{

	__SetPageUptodate(new_page);

	set_huge_pte_at(vma->vm_mm, addr, ptep, make_huge_pte(vma, new_page, 1));

	hugepage_add_new_anon_rmap(new_page, vma, addr);

	hugetlb_count_add(pages_per_huge_page(hstate_vma(vma)), vma->vm_mm);

	ClearHPageRestoreReserve(new_page);

	SetHPageMigratable(new_page);

}



int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,

			    struct vm_area_struct *vma)

{
@@ -3737,6 +3749,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, 
	bool cow = is_cow_mapping(vma->vm_flags);

	struct hstate *h = hstate_vma(vma);

	unsigned long sz = huge_page_size(h);

	unsigned long npages = pages_per_huge_page(h);

	struct address_space *mapping = vma->vm_file->f_mapping;

	struct mmu_notifier_range range;

	int ret = 0;
@@ -3785,6 +3798,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, 
		spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);

		entry = huge_ptep_get(src_pte);

		dst_entry = huge_ptep_get(dst_pte);

again:

		if (huge_pte_none(entry) || !huge_pte_none(dst_entry)) {

			/*

			 * Skip if src entry none.  Also, skip in the
@@ -3808,6 +3822,52 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, 
			}

			set_huge_swap_pte_at(dst, addr, dst_pte, entry, sz);

		} else {

			entry = huge_ptep_get(src_pte);

			ptepage = pte_page(entry);

			get_page(ptepage);



			/*

			 * This is a rare case where we see pinned hugetlb

			 * pages while they're prone to COW.  We need to do the

			 * COW earlier during fork.

			 *

			 * When pre-allocating the page or copying data, we

			 * need to be without the pgtable locks since we could

			 * sleep during the process.

			 */

			if (unlikely(page_needs_cow_for_dma(vma, ptepage))) {

				pte_t src_pte_old = entry;

				struct page *new;



				spin_unlock(src_ptl);

				spin_unlock(dst_ptl);

				/* Do not use reserve as it's private owned */

				new = alloc_huge_page(vma, addr, 1);

				if (IS_ERR(new)) {

					put_page(ptepage);

					ret = PTR_ERR(new);

					break;

				}

				copy_user_huge_page(new, ptepage, addr, vma,

						    npages);

				put_page(ptepage);



				/* Install the new huge page if src pte stable */

				dst_ptl = huge_pte_lock(h, dst, dst_pte);

				src_ptl = huge_pte_lockptr(h, src, src_pte);

				spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);

				entry = huge_ptep_get(src_pte);

				if (!pte_same(src_pte_old, entry)) {

					put_page(new);

					/* dst_entry won't change as in child */

					goto again;

				}

				hugetlb_install_page(vma, dst_pte, addr, new);

				spin_unlock(src_ptl);

				spin_unlock(dst_ptl);

				continue;

			}



			if (cow) {

				/*

				 * No need to notify as we are downgrading page
@@ -3818,12 +3878,10 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, 
				 */

				huge_ptep_set_wrprotect(src, addr, src_pte);

			}

			entry = huge_ptep_get(src_pte);

			ptepage = pte_page(entry);

			get_page(ptepage);



			page_dup_rmap(ptepage, true);

			set_huge_pte_at(dst, addr, dst_pte, entry);

			hugetlb_count_add(pages_per_huge_page(h), dst);

			hugetlb_count_add(npages, dst);

		}

		spin_unlock(src_ptl);

		spin_unlock(dst_ptl);