[PATCH 6.0 043/157] mm/khugepaged: fix GUP-fast interaction by sending IPI

Greg Kroah-Hartman
2022-12-12T13:37:27Z

From: Jann Horn <jannh@google.com>

commit 2ba99c5e08812494bc57f319fb562f527d9bacd8 upstream.

Since commit 70cbc3cc78a99 ("mm: gup: fix the fast GUP race against THP
collapse"), the lockless_pages_from_mm() fastpath rechecks the pmd_t to
ensure that the page table was not removed by khugepaged in between.

However, lockless_pages_from_mm() still requires that the page table is
not concurrently freed. Fix it by sending IPIs (if the architecture uses
semi-RCU-style page table freeing) before freeing/reusing page tables.

Link: https://lkml.kernel.org/r/20221129154730.2274278-2-jannh@google.com
Link: https://lkml.kernel.org/r/20221128180252.1684965-2-jannh@google.com
Link: https://lkml.kernel.org/r/20221125213714.4115729-2-jannh@google.com
Fixes: ba76149f47d8 ("thp: khugepaged")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[backported, no changes necessary]
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/asm-generic/tlb.h | 4 ++++
mm/khugepaged.c | 2 ++
mm/mmu_gather.c | 4 +---
3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 492dce43236e..cab7cfebf40b 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -222,12 +222,16 @@ extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
#define tlb_needs_table_invalidate() (true)
#endif

+void tlb_remove_table_sync_one(void);
+
#else

#ifdef tlb_needs_table_invalidate
#error tlb_needs_table_invalidate() requires MMU_GATHER_RCU_TABLE_FREE
#endif

+static inline void tlb_remove_table_sync_one(void) { }
+
#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 28d8459d7aae..1155d356d3ac 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1093,6 +1093,7 @@ static void collapse_huge_page(struct mm_struct *mm,
_pmd = pmdp_collapse_flush(vma, address, pmd);
spin_unlock(pmd_ptl);
mmu_notifier_invalidate_range_end(&range);
+ tlb_remove_table_sync_one();

spin_lock(pte_ptl);
isolated = __collapse_huge_page_isolate(vma, address, pte,
@@ -1391,6 +1392,7 @@ static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *v
lockdep_assert_held_write(&vma->anon_vma->root->rwsem);

pmd = pmdp_collapse_flush(vma, addr, pmdp);
+ tlb_remove_table_sync_one();
mm_dec_nr_ptes(mm);
page_table_check_pte_clear_range(mm, addr, pmd);
pte_free(mm, pmd_pgtable(pmd));
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index a71924bd38c0..ba7d26a291dd 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -152,7 +152,7 @@ static void tlb_remove_table_smp_sync(void *arg)
/* Simply deliver the interrupt */
}

-static void tlb_remove_table_sync_one(void)
+void tlb_remove_table_sync_one(void)
{
/*
* This isn't an RCU grace period and hence the page-tables cannot be
@@ -176,8 +176,6 @@ static void tlb_remove_table_free(struct mmu_table_batch *batch)

#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */

-static void tlb_remove_table_sync_one(void) { }
-
static void tlb_remove_table_free(struct mmu_table_batch *batch)
{
__tlb_remove_table_free(batch);
--
2.35.1