On Thu, Feb 20, 2025 at 9:40 PM David Hildenbrand david@redhat.com wrote:
On 19.02.25 19:58, Suren Baghdasaryan wrote:
On Wed, Feb 19, 2025 at 10:30 AM David Hildenbrand david@redhat.com wrote:
On 19.02.25 19:26, Suren Baghdasaryan wrote:
On Wed, Feb 19, 2025 at 3:25 AM Barry Song 21cnbao@gmail.com wrote:
From: Barry Song v-songbaohua@oppo.com
userfaultfd_move() checks whether the PTE entry is present or a swap entry.
- If the PTE entry is present, move_present_pte() handles folio
migration by setting:
src_folio->index = linear_page_index(dst_vma, dst_addr);
- If the PTE entry is a swap entry, move_swap_pte() simply copies
the PTE to the new dst_addr.
This approach is incorrect because even if the PTE is a swap entry, it can still reference a folio that remains in the swap cache.
If do_swap_page() is triggered, it may locate the folio in the swap cache. However, during add_rmap operations, a kernel panic can occur due to: page_pgoff(folio, page) != linear_page_index(vma, address)
Thanks for the report and reproducer!
$./a.out > /dev/null [ 13.336953] page: refcount:6 mapcount:1 mapping:00000000f43db19c index:0xffffaf150 pfn:0x4667c [ 13.337520] head: order:2 mapcount:1 entire_mapcount:0 nr_pages_mapped:1 pincount:0 [ 13.337716] memcg:ffff00000405f000 [ 13.337849] anon flags: 0x3fffc0000020459(locked|uptodate|dirty|owner_priv_1|head|swapbacked|node=0|zone=0|lastcpupid=0xffff) [ 13.338630] raw: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361 [ 13.338831] raw: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000 [ 13.339031] head: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361 [ 13.339204] head: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000 [ 13.339375] head: 03fffc0000000202 fffffdffc0199f01 ffffffff00000000 0000000000000001 [ 13.339546] head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000 [ 13.339736] page dumped because: VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address)) [ 13.340190] ------------[ cut here ]------------ [ 13.340316] kernel BUG at mm/rmap.c:1380! [ 13.340683] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP [ 13.340969] Modules linked in: [ 13.341257] CPU: 1 UID: 0 PID: 107 Comm: a.out Not tainted 6.14.0-rc3-gcf42737e247a-dirty #299 [ 13.341470] Hardware name: linux,dummy-virt (DT) [ 13.341671] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 13.341815] pc : __page_check_anon_rmap+0xa0/0xb0 [ 13.341920] lr : __page_check_anon_rmap+0xa0/0xb0 [ 13.342018] sp : ffff80008752bb20 [ 13.342093] x29: ffff80008752bb20 x28: fffffdffc0199f00 x27: 0000000000000001 [ 13.342404] x26: 0000000000000000 x25: 0000000000000001 x24: 0000000000000001 [ 13.342575] x23: 0000ffffaf0d0000 x22: 0000ffffaf0d0000 x21: fffffdffc0199f00 [ 13.342731] x20: fffffdffc0199f00 x19: ffff000006210700 x18: 00000000ffffffff [ 13.342881] x17: 6c203d2120296567 x16: 6170202c6f696c6f x15: 662866666f67705f [ 13.343033] x14: 6567617028454741 x13: 2929737365726464 x12: ffff800083728ab0 [ 13.343183] x11: ffff800082996bf8 x10: 0000000000000fd7 x9 : ffff80008011bc40 [ 13.343351] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000829eebf8 [ 13.343498] x5 : c0000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000 [ 13.343645] x2 : 0000000000000000 x1 : ffff0000062db980 x0 : 000000000000005f [ 13.343876] Call trace: [ 13.344045] __page_check_anon_rmap+0xa0/0xb0 (P) [ 13.344234] folio_add_anon_rmap_ptes+0x22c/0x320 [ 13.344333] do_swap_page+0x1060/0x1400 [ 13.344417] __handle_mm_fault+0x61c/0xbc8 [ 13.344504] handle_mm_fault+0xd8/0x2e8 [ 13.344586] do_page_fault+0x20c/0x770 [ 13.344673] do_translation_fault+0xb4/0xf0 [ 13.344759] do_mem_abort+0x48/0xa0 [ 13.344842] el0_da+0x58/0x130 [ 13.344914] el0t_64_sync_handler+0xc4/0x138 [ 13.345002] el0t_64_sync+0x1ac/0x1b0 [ 13.345208] Code: aa1503e0 f000f801 910f6021 97ff5779 (d4210000) [ 13.345504] ---[ end trace 0000000000000000 ]--- [ 13.345715] note: a.out[107] exited with irqs disabled [ 13.345954] note: a.out[107] exited with preempt_count 2
Fully fixing it would be quite complex, requiring similar handling of folios as done in move_present_pte.
How complex would that be? Is it a matter of adding folio_maybe_dma_pinned() checks, doing folio_move_anon_rmap() and folio->index = linear_page_index like in move_present_pte() or something more?
If the entry is pte_swp_exclusive(), and the folio is order-0, it cannot be pinned and we may be able to move it I think.
So all that's required is to check pte_swp_exclusive() and the folio size.
... in theory :) Not sure about the swap details.
Looking some more into it, I think we would have to perform all the folio and anon_vma locking and pinning that we do for present pages in move_pages_pte(). If that's correct then maybe treating swapcache pages like a present page inside move_pages_pte() would be simpler?
I'd be more in favor of not doing that. Maybe there are parts we can move out into helper functions instead, so we can reuse them?
I actually have a v2 ready. Maybe we can discuss if some of the code can be extracted as a helper based on the below before I send it formally?
I’d say there are many parts that can be shared with present PTE, but there are two major differences:
1. Page exclusivity – swapcache doesn’t require it (try_to_unmap_one has remove Exclusive flag;) 2. src_anon_vma and its lock – swapcache doesn’t require it（folio is not mapped）
Subject: [PATCH v2 Discussing with David] mm: Fix kernel crash when userfaultfd_move encounters swapcache
userfaultfd_move() checks whether the PTE entry is present or a swap entry.
- If the PTE entry is present, move_present_pte() handles folio migration by setting:
src_folio->index = linear_page_index(dst_vma, dst_addr);
- If the PTE entry is a swap entry, move_swap_pte() simply copies the PTE to the new dst_addr.
This approach is incorrect because, even if the PTE is a swap entry, it can still reference a folio that remains in the swap cache.
This exposes a race condition between steps 2 and 4: 1. add_to_swap: The folio is added to the swapcache. 2. try_to_unmap: PTEs are converted to swap entries. 3. pageout: The folio is written back. 4. Swapcache is cleared. If userfaultfd_move() happens in the window between step 2 and step 4, after the swap PTE is moved to the destination, accessing the destination triggers do_swap_page(), which may locate the folio in the swap cache. However, during add_rmap operations, a kernel panic can occur due to:
page_pgoff(folio, page) != linear_page_index(vma, address)
This happens because move_swap_pte() has never updated the index to match dst_vma and dst_addr.
$./a.out > /dev/null [ 13.336953] page: refcount:6 mapcount:1 mapping:00000000f43db19c index:0xffffaf150 pfn:0x4667c [ 13.337520] head: order:2 mapcount:1 entire_mapcount:0 nr_pages_mapped:1 pincount:0 [ 13.337716] memcg:ffff00000405f000 [ 13.337849] anon flags: 0x3fffc0000020459(locked|uptodate|dirty|owner_priv_1|head|swapbacked|node=0|zone=0|lastcpupid=0xffff) [ 13.338630] raw: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361 [ 13.338831] raw: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000 [ 13.339031] head: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361 [ 13.339204] head: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000 [ 13.339375] head: 03fffc0000000202 fffffdffc0199f01 ffffffff00000000 0000000000000001 [ 13.339546] head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000 [ 13.339736] page dumped because: VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address)) [ 13.340190] ------------[ cut here ]------------ [ 13.340316] kernel BUG at mm/rmap.c:1380! [ 13.340683] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP [ 13.340969] Modules linked in: [ 13.341257] CPU: 1 UID: 0 PID: 107 Comm: a.out Not tainted 6.14.0-rc3-gcf42737e247a-dirty #299 [ 13.341470] Hardware name: linux,dummy-virt (DT) [ 13.341671] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 13.341815] pc : __page_check_anon_rmap+0xa0/0xb0 [ 13.341920] lr : __page_check_anon_rmap+0xa0/0xb0 [ 13.342018] sp : ffff80008752bb20 [ 13.342093] x29: ffff80008752bb20 x28: fffffdffc0199f00 x27: 0000000000000001 [ 13.342404] x26: 0000000000000000 x25: 0000000000000001 x24: 0000000000000001 [ 13.342575] x23: 0000ffffaf0d0000 x22: 0000ffffaf0d0000 x21: fffffdffc0199f00 [ 13.342731] x20: fffffdffc0199f00 x19: ffff000006210700 x18: 00000000ffffffff [ 13.342881] x17: 6c203d2120296567 x16: 6170202c6f696c6f x15: 662866666f67705f [ 13.343033] x14: 6567617028454741 x13: 2929737365726464 x12: ffff800083728ab0 [ 13.343183] x11: ffff800082996bf8 x10: 0000000000000fd7 x9 : ffff80008011bc40 [ 13.343351] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000829eebf8 [ 13.343498] x5 : c0000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000 [ 13.343645] x2 : 0000000000000000 x1 : ffff0000062db980 x0 : 000000000000005f [ 13.343876] Call trace: [ 13.344045] __page_check_anon_rmap+0xa0/0xb0 (P) [ 13.344234] folio_add_anon_rmap_ptes+0x22c/0x320 [ 13.344333] do_swap_page+0x1060/0x1400 [ 13.344417] __handle_mm_fault+0x61c/0xbc8 [ 13.344504] handle_mm_fault+0xd8/0x2e8 [ 13.344586] do_page_fault+0x20c/0x770 [ 13.344673] do_translation_fault+0xb4/0xf0 [ 13.344759] do_mem_abort+0x48/0xa0 [ 13.344842] el0_da+0x58/0x130 [ 13.344914] el0t_64_sync_handler+0xc4/0x138 [ 13.345002] el0t_64_sync+0x1ac/0x1b0 [ 13.345208] Code: aa1503e0 f000f801 910f6021 97ff5779 (d4210000) [ 13.345504] ---[ end trace 0000000000000000 ]--- [ 13.345715] note: a.out[107] exited with irqs disabled [ 13.345954] note: a.out[107] exited with preempt_count 2
This patch also checks the swapcache when handling swap entries. If a match is found in the swapcache, it processes it similarly to a present PTE. However, there are some differences. For example, the folio is no longer exclusive because folio_try_share_anon_rmap_pte() is performed during unmapping. Furthermore, in the case of swapcache, the folio has already been unmapped, eliminating the risk of concurrent rmap walks and removing the need to acquire src_folio's anon_vma or lock.
Note that for large folios, in the swapcache handling path, we still frequently encounter -EBUSY returns because split_folio() returns -EBUSY when the folio is under writeback. That is not an urgent fix, so a following patch will address it.
Fixes: adef440691bab ("userfaultfd: UFFDIO_MOVE uABI") Cc: Andrea Arcangeli aarcange@redhat.com Cc: Suren Baghdasaryan surenb@google.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Axel Rasmussen axelrasmussen@google.com Cc: Brian Geffon bgeffon@google.com Cc: Christian Brauner brauner@kernel.org Cc: David Hildenbrand david@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Jann Horn jannh@google.com Cc: Kalesh Singh kaleshsingh@google.com Cc: Liam R. Howlett Liam.Howlett@oracle.com Cc: Lokesh Gidra lokeshgidra@google.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Michal Hocko mhocko@suse.com Cc: Mike Rapoport (IBM) rppt@kernel.org Cc: Nicolas Geoffray ngeoffray@google.com Cc: Peter Xu peterx@redhat.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: Shuah Khan shuah@kernel.org Cc: ZhangPeng zhangpeng362@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Barry Song v-songbaohua@oppo.com --- mm/userfaultfd.c | 228 +++++++++++++++++++++++++++-------------------- 1 file changed, 133 insertions(+), 95 deletions(-)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 867898c4e30b..e5718835a964 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -18,6 +18,7 @@ #include <asm/tlbflush.h> #include <asm/tlb.h> #include "internal.h" +#include "swap.h"
static __always_inline bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end) @@ -1025,7 +1026,7 @@ static inline bool is_pte_pages_stable(pte_t *dst_pte, pte_t *src_pte, pmd_same(dst_pmdval, pmdp_get_lockless(dst_pmd)); }
-static int move_present_pte(struct mm_struct *mm, +static int move_pte_and_folio(struct mm_struct *mm, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long dst_addr, unsigned long src_addr, @@ -1046,7 +1047,7 @@ static int move_present_pte(struct mm_struct *mm, } if (folio_test_large(src_folio) || folio_maybe_dma_pinned(src_folio) || - !PageAnonExclusive(&src_folio->page)) { + (pte_present(orig_src_pte) && !PageAnonExclusive(&src_folio->page))) { err = -EBUSY; goto out; } @@ -1062,10 +1063,13 @@ static int move_present_pte(struct mm_struct *mm, folio_move_anon_rmap(src_folio, dst_vma); src_folio->index = linear_page_index(dst_vma, dst_addr);
- orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot); - /* Follow mremap() behavior and treat the entry dirty after the move */ - orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma); - + if (pte_present(orig_src_pte)) { + orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot); + /* Follow mremap() behavior and treat the entry dirty after the move */ + orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma); + } else { /* swap entry */ + orig_dst_pte = orig_src_pte; + } set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte); out: double_pt_unlock(dst_ptl, src_ptl); @@ -1079,9 +1083,6 @@ static int move_swap_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl) { - if (!pte_swp_exclusive(orig_src_pte)) - return -EBUSY; - double_pt_lock(dst_ptl, src_ptl);
if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, @@ -1137,6 +1138,7 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, __u64 mode) { swp_entry_t entry; + struct swap_info_struct *si = NULL; pte_t orig_src_pte, orig_dst_pte; pte_t src_folio_pte; spinlock_t *src_ptl, *dst_ptl; @@ -1220,122 +1222,156 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, goto out; }
- if (pte_present(orig_src_pte)) { - if (is_zero_pfn(pte_pfn(orig_src_pte))) { - err = move_zeropage_pte(mm, dst_vma, src_vma, - dst_addr, src_addr, dst_pte, src_pte, - orig_dst_pte, orig_src_pte, - dst_pmd, dst_pmdval, dst_ptl, src_ptl); + if (!pte_present(orig_src_pte)) { + entry = pte_to_swp_entry(orig_src_pte); + if (is_migration_entry(entry)) { + pte_unmap(&orig_src_pte); + pte_unmap(&orig_dst_pte); + src_pte = dst_pte = NULL; + migration_entry_wait(mm, src_pmd, src_addr); + err = -EAGAIN; + goto out; + } + + if (non_swap_entry(entry)) { + err = -EFAULT; + goto out; + } + + if (!pte_swp_exclusive(orig_src_pte)) { + err = -EBUSY; + goto out; + } + /* Prevent swapoff from happening to us. */ + if (!si) + si = get_swap_device(entry); + if (unlikely(!si)) { + err = -EAGAIN; goto out; } + } + + if (pte_present(orig_src_pte) && is_zero_pfn(pte_pfn(orig_src_pte))) { + err = move_zeropage_pte(mm, dst_vma, src_vma, + dst_addr, src_addr, dst_pte, src_pte, + orig_dst_pte, orig_src_pte, + dst_pmd, dst_pmdval, dst_ptl, src_ptl); + goto out; + } + + /* + * Pin and lock both source folio and anon_vma. Since we are in + * RCU read section, we can't block, so on contention have to + * unmap the ptes, obtain the lock and retry. + */ + if (!src_folio) { + struct folio *folio;
/* - * Pin and lock both source folio and anon_vma. Since we are in - * RCU read section, we can't block, so on contention have to - * unmap the ptes, obtain the lock and retry. + * Pin the page while holding the lock to be sure the + * page isn't freed under us */ - if (!src_folio) { - struct folio *folio; + spin_lock(src_ptl); + if (!pte_same(orig_src_pte, ptep_get(src_pte))) { + spin_unlock(src_ptl); + err = -EAGAIN; + goto out; + }
- /* - * Pin the page while holding the lock to be sure the - * page isn't freed under us - */ - spin_lock(src_ptl); - if (!pte_same(orig_src_pte, ptep_get(src_pte))) { + if (pte_present(orig_src_pte)) { + folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); + if (!folio) { spin_unlock(src_ptl); - err = -EAGAIN; + err = -EBUSY; goto out; } - - folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); - if (!folio || !PageAnonExclusive(&folio->page)) { + if (!PageAnonExclusive(&folio->page)) { spin_unlock(src_ptl); err = -EBUSY; goto out; } - folio_get(folio); - src_folio = folio; - src_folio_pte = orig_src_pte; - spin_unlock(src_ptl); - - if (!folio_trylock(src_folio)) { - pte_unmap(&orig_src_pte); - pte_unmap(&orig_dst_pte); - src_pte = dst_pte = NULL; - /* now we can block and wait */ - folio_lock(src_folio); - goto retry; - } - - if (WARN_ON_ONCE(!folio_test_anon(src_folio))) { - err = -EBUSY; + } else { + /* + * Check if swapcache exists. + * If it does, we need to move the folio + * even if the PTE is a swap entry. + */ + folio = filemap_get_folio(swap_address_space(entry), + swap_cache_index(entry)); + if (IS_ERR(folio)) { + spin_unlock(src_ptl); + err = move_swap_pte(mm, dst_addr, src_addr, dst_pte, src_pte, + orig_dst_pte, orig_src_pte, dst_pmd, + dst_pmdval, dst_ptl, src_ptl); goto out; } }
- /* at this point we have src_folio locked */ - if (folio_test_large(src_folio)) { - /* split_folio() can block */ + src_folio = folio; + src_folio_pte = orig_src_pte; + spin_unlock(src_ptl); + + if (!folio_trylock(src_folio)) { pte_unmap(&orig_src_pte); pte_unmap(&orig_dst_pte); src_pte = dst_pte = NULL; - err = split_folio(src_folio); - if (err) - goto out; - /* have to reacquire the folio after it got split */ - folio_unlock(src_folio); - folio_put(src_folio); - src_folio = NULL; + /* now we can block and wait */ + folio_lock(src_folio); goto retry; }
- if (!src_anon_vma) { - /* - * folio_referenced walks the anon_vma chain - * without the folio lock. Serialize against it with - * the anon_vma lock, the folio lock is not enough. - */ - src_anon_vma = folio_get_anon_vma(src_folio); - if (!src_anon_vma) { - /* page was unmapped from under us */ - err = -EAGAIN; - goto out; - } - if (!anon_vma_trylock_write(src_anon_vma)) { - pte_unmap(&orig_src_pte); - pte_unmap(&orig_dst_pte); - src_pte = dst_pte = NULL; - /* now we can block and wait */ - anon_vma_lock_write(src_anon_vma); - goto retry; - } + if (WARN_ON_ONCE(!folio_test_anon(src_folio))) { + err = -EBUSY; + goto out; } + }
- err = move_present_pte(mm, dst_vma, src_vma, - dst_addr, src_addr, dst_pte, src_pte, - orig_dst_pte, orig_src_pte, dst_pmd, - dst_pmdval, dst_ptl, src_ptl, src_folio); - } else { - entry = pte_to_swp_entry(orig_src_pte); - if (non_swap_entry(entry)) { - if (is_migration_entry(entry)) { - pte_unmap(&orig_src_pte); - pte_unmap(&orig_dst_pte); - src_pte = dst_pte = NULL; - migration_entry_wait(mm, src_pmd, src_addr); - err = -EAGAIN; - } else - err = -EFAULT; + /* at this point we have src_folio locked */ + if (folio_test_large(src_folio)) { + /* split_folio() can block */ + pte_unmap(&orig_src_pte); + pte_unmap(&orig_dst_pte); + src_pte = dst_pte = NULL; + err = split_folio(src_folio); + if (err) goto out; - } + /* have to reacquire the folio after it got split */ + folio_unlock(src_folio); + folio_put(src_folio); + src_folio = NULL; + goto retry; + }
- err = move_swap_pte(mm, dst_addr, src_addr, dst_pte, src_pte, - orig_dst_pte, orig_src_pte, dst_pmd, - dst_pmdval, dst_ptl, src_ptl); + if (!src_anon_vma && pte_present(orig_src_pte)) { + /* + * folio_referenced walks the anon_vma chain + * without the folio lock. Serialize against it with + * the anon_vma lock, the folio lock is not enough. + * In the swapcache case, the folio has been unmapped, + * so there is no concurrent rmap walk. + */ + src_anon_vma = folio_get_anon_vma(src_folio); + if (!src_anon_vma) { + /* page was unmapped from under us */ + err = -EAGAIN; + goto out; + } + if (!anon_vma_trylock_write(src_anon_vma)) { + pte_unmap(&orig_src_pte); + pte_unmap(&orig_dst_pte); + src_pte = dst_pte = NULL; + /* now we can block and wait */ + anon_vma_lock_write(src_anon_vma); + goto retry; + } }
+ err = move_pte_and_folio(mm, dst_vma, src_vma, + dst_addr, src_addr, dst_pte, src_pte, + orig_dst_pte, orig_src_pte, dst_pmd, + dst_pmdval, dst_ptl, src_ptl, src_folio); + out: if (src_anon_vma) { anon_vma_unlock_write(src_anon_vma); @@ -1351,6 +1387,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pte_unmap(src_pte); mmu_notifier_invalidate_range_end(&range);
+ if (si) + put_swap_device(si); return err; }