Commit f45ec5ff authored by Peter Xu's avatar Peter Xu Committed by Linus Torvalds
Browse files

userfaultfd: wp: support swap and page migration 



For either swap and page migration, we all use the bit 2 of the entry to
identify whether this entry is uffd write-protected.  It plays a similar
role as the existing soft dirty bit in swap entries but only for keeping
the uffd-wp tracking for a specific PTE/PMD.

Something special here is that when we want to recover the uffd-wp bit
from a swap/migration entry to the PTE bit we'll also need to take care of
the _PAGE_RW bit and make sure it's cleared, otherwise even with the
_PAGE_UFFD_WP bit we can't trap it at all.

In change_pte_range() we do nothing for uffd if the PTE is a swap entry.
That can lead to data mismatch if the page that we are going to write
protect is swapped out when sending the UFFDIO_WRITEPROTECT.  This patch
also applies/removes the uffd-wp bit even for the swap entries.

Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-11-peterx@redhat.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2e3d5dc5

include/linux/swapops.h

+2 −0
Original line number Diff line number Diff line
@@ -68,6 +68,8 @@ static inline swp_entry_t pte_to_swp_entry(pte_t pte) 


	if (pte_swp_soft_dirty(pte))

		pte = pte_swp_clear_soft_dirty(pte);

	if (pte_swp_uffd_wp(pte))

		pte = pte_swp_clear_uffd_wp(pte);

	arch_entry = __pte_to_swp_entry(pte);

	return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));

}

mm/huge_memory.c

+3 −0
Original line number Diff line number Diff line
@@ -2297,6 +2297,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 
		write = is_write_migration_entry(entry);

		young = false;

		soft_dirty = pmd_swp_soft_dirty(old_pmd);

		uffd_wp = pmd_swp_uffd_wp(old_pmd);

	} else {

		page = pmd_page(old_pmd);

		if (pmd_dirty(old_pmd))
@@ -2329,6 +2330,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 
			entry = swp_entry_to_pte(swp_entry);

			if (soft_dirty)

				entry = pte_swp_mksoft_dirty(entry);

			if (uffd_wp)

				entry = pte_swp_mkuffd_wp(entry);

		} else {

			entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));

			entry = maybe_mkwrite(entry, vma);

mm/memory.c

+8 −0
Original line number Diff line number Diff line
@@ -733,6 +733,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
				pte = swp_entry_to_pte(entry);

				if (pte_swp_soft_dirty(*src_pte))

					pte = pte_swp_mksoft_dirty(pte);

				if (pte_swp_uffd_wp(*src_pte))

					pte = pte_swp_mkuffd_wp(pte);

				set_pte_at(src_mm, addr, src_pte, pte);

			}

		} else if (is_device_private_entry(entry)) {
@@ -762,6 +764,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
			    is_cow_mapping(vm_flags)) {

				make_device_private_entry_read(&entry);

				pte = swp_entry_to_pte(entry);

				if (pte_swp_uffd_wp(*src_pte))

					pte = pte_swp_mkuffd_wp(pte);

				set_pte_at(src_mm, addr, src_pte, pte);

			}

		}
@@ -3098,6 +3102,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 
	flush_icache_page(vma, page);

	if (pte_swp_soft_dirty(vmf->orig_pte))

		pte = pte_mksoft_dirty(pte);

	if (pte_swp_uffd_wp(vmf->orig_pte)) {

		pte = pte_mkuffd_wp(pte);

		pte = pte_wrprotect(pte);

	}

	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);

	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);

	vmf->orig_pte = pte;

mm/migrate.c

+6 −0
Original line number Diff line number Diff line
@@ -243,11 +243,15 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma, 
		entry = pte_to_swp_entry(*pvmw.pte);

		if (is_write_migration_entry(entry))

			pte = maybe_mkwrite(pte, vma);

		else if (pte_swp_uffd_wp(*pvmw.pte))

			pte = pte_mkuffd_wp(pte);



		if (unlikely(is_zone_device_page(new))) {

			if (is_device_private_page(new)) {

				entry = make_device_private_entry(new, pte_write(pte));

				pte = swp_entry_to_pte(entry);

				if (pte_swp_uffd_wp(*pvmw.pte))

					pte = pte_mkuffd_wp(pte);

			}

		}
@@ -2338,6 +2342,8 @@ again: 
			swp_pte = swp_entry_to_pte(entry);

			if (pte_soft_dirty(pte))

				swp_pte = pte_swp_mksoft_dirty(swp_pte);

			if (pte_uffd_wp(pte))

				swp_pte = pte_swp_mkuffd_wp(swp_pte);

			set_pte_at(mm, addr, ptep, swp_pte);



			/*

mm/mprotect.c

+17 −11
Original line number Diff line number Diff line
@@ -139,11 +139,11 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 
			}

			ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);

			pages++;

		} else if (IS_ENABLED(CONFIG_MIGRATION)) {

		} else if (is_swap_pte(oldpte)) {

			swp_entry_t entry = pte_to_swp_entry(oldpte);

			pte_t newpte;



			if (is_write_migration_entry(entry)) {

				pte_t newpte;

				/*

				 * A protection check is difficult so

				 * just be safe and disable write
@@ -152,22 +152,28 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 
				newpte = swp_entry_to_pte(entry);

				if (pte_swp_soft_dirty(oldpte))

					newpte = pte_swp_mksoft_dirty(newpte);

				set_pte_at(vma->vm_mm, addr, pte, newpte);



				pages++;

			}



			if (is_write_device_private_entry(entry)) {

				pte_t newpte;



				if (pte_swp_uffd_wp(oldpte))

					newpte = pte_swp_mkuffd_wp(newpte);

			} else if (is_write_device_private_entry(entry)) {

				/*

				 * We do not preserve soft-dirtiness. See

				 * copy_one_pte() for explanation.

				 */

				make_device_private_entry_read(&entry);

				newpte = swp_entry_to_pte(entry);

				set_pte_at(vma->vm_mm, addr, pte, newpte);

				if (pte_swp_uffd_wp(oldpte))

					newpte = pte_swp_mkuffd_wp(newpte);

			} else {

				newpte = oldpte;

			}



			if (uffd_wp)

				newpte = pte_swp_mkuffd_wp(newpte);

			else if (uffd_wp_resolve)

				newpte = pte_swp_clear_uffd_wp(newpte);



			if (!pte_same(oldpte, newpte)) {

				set_pte_at(vma->vm_mm, addr, pte, newpte);

				pages++;

			}

		}

CRA Git | Maintained and supported by SUSTech CRA and CCSE