| Message ID | 20250226001400.9129-1-21cnbao@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] mm: Fix kernel BUG when userfaultfd_move encounters swapcache | expand |
On Wed, Feb 26, 2025 at 01:14:00PM +1300, Barry Song 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. > > This creates a race window 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() occurs in the window between steps 2 and 4, > after the swap PTE has been moved to the destination, accessing the > destination triggers do_swap_page(), which may locate the folio in > the swapcache. However, since the folio's index has not been updated > to match the destination VMA, do_swap_page() will detect a mismatch. > > This can result in two critical issues depending on the system > configuration. > > If KSM is disabled, both small and large folios can trigger a BUG > during the add_rmap operation due to: > > page_pgoff(folio, page) != linear_page_index(vma, address) > > [ 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 > > If KSM is enabled, Peter Xu also discovered that do_swap_page() may > trigger an unexpected CoW operation for small folios because > ksm_might_need_to_copy() allocates a new folio when the folio index > does not match linear_page_index(vma, addr). > > 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 directly > return -EBUSY since split_folio() will return -EBUSY regardless if > the folio is under writeback or unmapped. This is not an urgent issue, > so a follow-up patch may address it separately. > > 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: Tangquan Zheng <zhengtangquan@oppo.com> > Cc: <stable@vger.kernel.org> > Signed-off-by: Barry Song <v-songbaohua@oppo.com> Acked-by: Peter Xu <peterx@redhat.com> Some nitpicks below, maybe no worth for a repost.. > --- > mm/userfaultfd.c | 76 ++++++++++++++++++++++++++++++++++++++++++------ > 1 file changed, 67 insertions(+), 9 deletions(-) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 867898c4e30b..2df5d100e76d 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) > @@ -1072,16 +1073,14 @@ static int move_present_pte(struct mm_struct *mm, > return err; > } > > -static int move_swap_pte(struct mm_struct *mm, > +static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, > unsigned long dst_addr, unsigned long src_addr, > pte_t *dst_pte, pte_t *src_pte, > pte_t orig_dst_pte, pte_t orig_src_pte, > pmd_t *dst_pmd, pmd_t dst_pmdval, > - spinlock_t *dst_ptl, spinlock_t *src_ptl) > + spinlock_t *dst_ptl, spinlock_t *src_ptl, > + struct folio *src_folio) > { > - 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, > @@ -1090,10 +1089,20 @@ static int move_swap_pte(struct mm_struct *mm, > return -EAGAIN; > } > > + /* > + * The src_folio resides in the swapcache, requiring an update to its > + * index and mapping to align with the dst_vma, where a swap-in may > + * occur and hit the swapcache after moving the PTE. > + */ > + if (src_folio) { > + folio_move_anon_rmap(src_folio, dst_vma); > + src_folio->index = linear_page_index(dst_vma, dst_addr); > + } > + > orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); > set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); > - double_pt_unlock(dst_ptl, src_ptl); > > + double_pt_unlock(dst_ptl, src_ptl); Unnecessary line move. > return 0; > } > > @@ -1137,6 +1146,7 @@ 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; > @@ -1318,6 +1328,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > orig_dst_pte, orig_src_pte, dst_pmd, > dst_pmdval, dst_ptl, src_ptl, src_folio); > } else { > + struct folio *folio = NULL; > + > entry = pte_to_swp_entry(orig_src_pte); > if (non_swap_entry(entry)) { > if (is_migration_entry(entry)) { > @@ -1331,9 +1343,53 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > goto out; > } > > - 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 (!pte_swp_exclusive(orig_src_pte)) { > + err = -EBUSY; > + goto out; > + } > + > + si = get_swap_device(entry); > + if (unlikely(!si)) { > + err = -EAGAIN; > + goto out; > + } > + /* > + * Verify the existence of the swapcache. If present, the folio's > + * index and mapping must be updated even when the PTE is a swap > + * entry. The anon_vma lock is not taken during this process since > + * the folio has already been unmapped, and the swap entry is > + * exclusive, preventing rmap walks. > + * > + * For large folios, return -EBUSY immediately, as split_folio() > + * also returns -EBUSY when attempting to split unmapped large > + * folios in the swapcache. This issue needs to be resolved > + * separately to allow proper handling. > + */ > + if (!src_folio) > + folio = filemap_get_folio(swap_address_space(entry), > + swap_cache_index(entry)); > + if (!IS_ERR_OR_NULL(folio)) { > + if (folio && folio_test_large(folio)) { Can drop this folio check as it just did check "!IS_ERR_OR_NULL(folio)".. > + err = -EBUSY; > + folio_put(folio); > + goto out; > + } > + src_folio = folio; > + src_folio_pte = orig_src_pte; > + 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); > + put_swap_device(si); > + si = NULL; Not sure if it can do any harm, but maybe still nicer to put swap before locking folio. Thanks, > + goto retry; > + } > + } > + err = move_swap_pte(mm, dst_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: > @@ -1350,6 +1406,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > if (src_pte) > pte_unmap(src_pte); > mmu_notifier_invalidate_range_end(&range); > + if (si) > + put_swap_device(si); > > return err; > } > -- > 2.39.3 (Apple Git-146) >
On Wed, Feb 26, 2025 at 2:00 PM Peter Xu <peterx@redhat.com> wrote: > > Acked-by: Peter Xu <peterx@redhat.com> > Thanks! > Some nitpicks below, maybe no worth for a repost.. Hi Andrew, Could you please help squash the below change? From 42273506ba00723151e3a08b4ffd3f2c303e7ccc Mon Sep 17 00:00:00 2001 From: Barry Song <v-songbaohua@oppo.com> Date: Wed, 26 Feb 2025 15:22:17 +1300 Subject: [PATCH] minor cleanup according to Peter Xu According to Peter Xu: 1. Unnecessary line move. 2. Can drop this folio check as it just did check "!IS_ERR_OR_NULL(folio)" 3. Not sure if it can do any harm, but maybe still nicer to put swap before locking folio. Signed-off-by: Barry Song <v-songbaohua@oppo.com> --- mm/userfaultfd.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 2df5d100e76d..2955e20f86bf 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1101,8 +1101,8 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); - double_pt_unlock(dst_ptl, src_ptl); + return 0; } @@ -1369,7 +1369,7 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, folio = filemap_get_folio(swap_address_space(entry), swap_cache_index(entry)); if (!IS_ERR_OR_NULL(folio)) { - if (folio && folio_test_large(folio)) { + if (folio_test_large(folio)) { err = -EBUSY; folio_put(folio); goto out; @@ -1380,10 +1380,10 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, 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); put_swap_device(si); si = NULL; + /* now we can block and wait */ + folio_lock(src_folio); goto retry; } }
On Tue, Feb 25, 2025 at 5:00 PM Peter Xu <peterx@redhat.com> wrote: > > On Wed, Feb 26, 2025 at 01:14:00PM +1300, Barry Song 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. > > > > This creates a race window 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() occurs in the window between steps 2 and 4, > > after the swap PTE has been moved to the destination, accessing the > > destination triggers do_swap_page(), which may locate the folio in > > the swapcache. However, since the folio's index has not been updated > > to match the destination VMA, do_swap_page() will detect a mismatch. > > > > This can result in two critical issues depending on the system > > configuration. > > > > If KSM is disabled, both small and large folios can trigger a BUG > > during the add_rmap operation due to: > > > > page_pgoff(folio, page) != linear_page_index(vma, address) > > > > [ 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 > > > > If KSM is enabled, Peter Xu also discovered that do_swap_page() may > > trigger an unexpected CoW operation for small folios because > > ksm_might_need_to_copy() allocates a new folio when the folio index > > does not match linear_page_index(vma, addr). > > > > 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 directly > > return -EBUSY since split_folio() will return -EBUSY regardless if > > the folio is under writeback or unmapped. This is not an urgent issue, > > so a follow-up patch may address it separately. > > > > 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: Tangquan Zheng <zhengtangquan@oppo.com> > > Cc: <stable@vger.kernel.org> > > Signed-off-by: Barry Song <v-songbaohua@oppo.com> > > Acked-by: Peter Xu <peterx@redhat.com> > > Some nitpicks below, maybe no worth for a repost.. With Peter's nits addressed, Reviewed-by: Suren Baghdasaryan <surenb@google.com> Thanks! > > > --- > > mm/userfaultfd.c | 76 ++++++++++++++++++++++++++++++++++++++++++------ > > 1 file changed, 67 insertions(+), 9 deletions(-) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 867898c4e30b..2df5d100e76d 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) > > @@ -1072,16 +1073,14 @@ static int move_present_pte(struct mm_struct *mm, > > return err; > > } > > > > -static int move_swap_pte(struct mm_struct *mm, > > +static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, > > unsigned long dst_addr, unsigned long src_addr, > > pte_t *dst_pte, pte_t *src_pte, > > pte_t orig_dst_pte, pte_t orig_src_pte, > > pmd_t *dst_pmd, pmd_t dst_pmdval, > > - spinlock_t *dst_ptl, spinlock_t *src_ptl) > > + spinlock_t *dst_ptl, spinlock_t *src_ptl, > > + struct folio *src_folio) > > { > > - 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, > > @@ -1090,10 +1089,20 @@ static int move_swap_pte(struct mm_struct *mm, > > return -EAGAIN; > > } > > > > + /* > > + * The src_folio resides in the swapcache, requiring an update to its > > + * index and mapping to align with the dst_vma, where a swap-in may > > + * occur and hit the swapcache after moving the PTE. > > + */ > > + if (src_folio) { > > + folio_move_anon_rmap(src_folio, dst_vma); > > + src_folio->index = linear_page_index(dst_vma, dst_addr); > > + } > > + > > orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); > > set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); > > - double_pt_unlock(dst_ptl, src_ptl); > > > > + double_pt_unlock(dst_ptl, src_ptl); > > Unnecessary line move. > > > return 0; > > } > > > > @@ -1137,6 +1146,7 @@ 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; > > @@ -1318,6 +1328,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > > orig_dst_pte, orig_src_pte, dst_pmd, > > dst_pmdval, dst_ptl, src_ptl, src_folio); > > } else { > > + struct folio *folio = NULL; > > + > > entry = pte_to_swp_entry(orig_src_pte); > > if (non_swap_entry(entry)) { > > if (is_migration_entry(entry)) { > > @@ -1331,9 +1343,53 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > > goto out; > > } > > > > - 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 (!pte_swp_exclusive(orig_src_pte)) { > > + err = -EBUSY; > > + goto out; > > + } > > + > > + si = get_swap_device(entry); > > + if (unlikely(!si)) { > > + err = -EAGAIN; > > + goto out; > > + } > > + /* > > + * Verify the existence of the swapcache. If present, the folio's > > + * index and mapping must be updated even when the PTE is a swap > > + * entry. The anon_vma lock is not taken during this process since > > + * the folio has already been unmapped, and the swap entry is > > + * exclusive, preventing rmap walks. > > + * > > + * For large folios, return -EBUSY immediately, as split_folio() > > + * also returns -EBUSY when attempting to split unmapped large > > + * folios in the swapcache. This issue needs to be resolved > > + * separately to allow proper handling. > > + */ > > + if (!src_folio) > > + folio = filemap_get_folio(swap_address_space(entry), > > + swap_cache_index(entry)); > > + if (!IS_ERR_OR_NULL(folio)) { > > + if (folio && folio_test_large(folio)) { > > Can drop this folio check as it just did check "!IS_ERR_OR_NULL(folio)".. > > > + err = -EBUSY; > > + folio_put(folio); > > + goto out; > > + } > > + src_folio = folio; > > + src_folio_pte = orig_src_pte; > > + 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); > > + put_swap_device(si); > > + si = NULL; > > Not sure if it can do any harm, but maybe still nicer to put swap before > locking folio. > > Thanks, > > > + goto retry; > > + } > > + } > > + err = move_swap_pte(mm, dst_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: > > @@ -1350,6 +1406,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, > > if (src_pte) > > pte_unmap(src_pte); > > mmu_notifier_invalidate_range_end(&range); > > + if (si) > > + put_swap_device(si); > > > > return err; > > } > > -- > > 2.39.3 (Apple Git-146) > > > > -- > Peter Xu >
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 867898c4e30b..2df5d100e76d 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) @@ -1072,16 +1073,14 @@ static int move_present_pte(struct mm_struct *mm, return err; } -static int move_swap_pte(struct mm_struct *mm, +static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, pmd_t *dst_pmd, pmd_t dst_pmdval, - spinlock_t *dst_ptl, spinlock_t *src_ptl) + spinlock_t *dst_ptl, spinlock_t *src_ptl, + struct folio *src_folio) { - 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, @@ -1090,10 +1089,20 @@ static int move_swap_pte(struct mm_struct *mm, return -EAGAIN; } + /* + * The src_folio resides in the swapcache, requiring an update to its + * index and mapping to align with the dst_vma, where a swap-in may + * occur and hit the swapcache after moving the PTE. + */ + if (src_folio) { + folio_move_anon_rmap(src_folio, dst_vma); + src_folio->index = linear_page_index(dst_vma, dst_addr); + } + orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); - double_pt_unlock(dst_ptl, src_ptl); + double_pt_unlock(dst_ptl, src_ptl); return 0; } @@ -1137,6 +1146,7 @@ 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; @@ -1318,6 +1328,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval, dst_ptl, src_ptl, src_folio); } else { + struct folio *folio = NULL; + entry = pte_to_swp_entry(orig_src_pte); if (non_swap_entry(entry)) { if (is_migration_entry(entry)) { @@ -1331,9 +1343,53 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, goto out; } - 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 (!pte_swp_exclusive(orig_src_pte)) { + err = -EBUSY; + goto out; + } + + si = get_swap_device(entry); + if (unlikely(!si)) { + err = -EAGAIN; + goto out; + } + /* + * Verify the existence of the swapcache. If present, the folio's + * index and mapping must be updated even when the PTE is a swap + * entry. The anon_vma lock is not taken during this process since + * the folio has already been unmapped, and the swap entry is + * exclusive, preventing rmap walks. + * + * For large folios, return -EBUSY immediately, as split_folio() + * also returns -EBUSY when attempting to split unmapped large + * folios in the swapcache. This issue needs to be resolved + * separately to allow proper handling. + */ + if (!src_folio) + folio = filemap_get_folio(swap_address_space(entry), + swap_cache_index(entry)); + if (!IS_ERR_OR_NULL(folio)) { + if (folio && folio_test_large(folio)) { + err = -EBUSY; + folio_put(folio); + goto out; + } + src_folio = folio; + src_folio_pte = orig_src_pte; + 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); + put_swap_device(si); + si = NULL; + goto retry; + } + } + err = move_swap_pte(mm, dst_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: @@ -1350,6 +1406,8 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, if (src_pte) pte_unmap(src_pte); mmu_notifier_invalidate_range_end(&range); + if (si) + put_swap_device(si); return err; }