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Subject[PATCH v5 15/25] userfaultfd: wp: support swap and page migration
Date
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: Peter Xu <peterx@redhat.com>
---
include/linux/swapops.h | 2 ++
mm/huge_memory.c | 3 +++
mm/memory.c | 8 ++++++++
mm/migrate.c | 6 ++++++
mm/mprotect.c | 28 +++++++++++++++++-----------
mm/rmap.c | 6 ++++++
6 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 4d961668e5fc..0c2923b1cdb7 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -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));
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 757975920df8..eae25c58db9d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2221,6 +2221,7 @@ 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))
@@ -2253,6 +2254,8 @@ 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);
diff --git a/mm/memory.c b/mm/memory.c
index 8c69257d6ef1..28e9342d00cc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -738,6 +738,8 @@ 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)) {
@@ -767,6 +769,8 @@ 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);
}
}
@@ -2930,6 +2934,10 @@ 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;
diff --git a/mm/migrate.c b/mm/migrate.c
index f2ecc2855a12..d8f1f6d13960 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -241,11 +241,15 @@ 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);
} else if (is_device_public_page(new)) {
pte = pte_mkdevmap(pte);
}
@@ -2306,6 +2310,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
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);

/*
diff --git a/mm/mprotect.c b/mm/mprotect.c
index c7066d7384e3..a63737d9884e 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -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++;
}
}
diff --git a/mm/rmap.c b/mm/rmap.c
index e5dfe2ae6b0d..dedde54dadb7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1471,6 +1471,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
+ if (pte_uffd_wp(pteval))
+ swp_pte = pte_swp_mkuffd_wp(swp_pte);
set_pte_at(mm, pvmw.address, pvmw.pte, swp_pte);
/*
* No need to invalidate here it will synchronize on
@@ -1563,6 +1565,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
+ if (pte_uffd_wp(pteval))
+ swp_pte = pte_swp_mkuffd_wp(swp_pte);
set_pte_at(mm, address, pvmw.pte, swp_pte);
/*
* No need to invalidate here it will synchronize on
@@ -1629,6 +1633,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
+ if (pte_uffd_wp(pteval))
+ swp_pte = pte_swp_mkuffd_wp(swp_pte);
set_pte_at(mm, address, pvmw.pte, swp_pte);
/* Invalidate as we cleared the pte */
mmu_notifier_invalidate_range(mm, address,
--
2.21.0
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