On Thu, Feb 20, 2025 at 9:40 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 19.02.25 19:58, Suren Baghdasaryan wrote:
> > On Wed, Feb 19, 2025 at 10:30 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
> >>
> >> On 19.02.25 19:26, Suren Baghdasaryan wrote:
> >>> On Wed, Feb 19, 2025 at 3:25 AM Barry Song <21cnbao@xxxxxxxxx> wrote:
> >>>>
> >>>> From: Barry Song <v-songbaohua@xxxxxxxx>
> >>>>
> >>>> 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@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Nicolas Geoffray <ngeoffray@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: ZhangPeng <zhangpeng362@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
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;
}
--
2.39.3 (Apple Git-146)
>
> --
> Cheers,
>
> David / dhildenb
>
