[PATCH 5.4 18/67] mm/khugepaged: fix GUP-fast interaction by sending IPI

Greg Kroah-Hartman
2022-12-12T13:20:50Z

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>
[manual backport: two of the three places in khugepaged that can free
ptes were refactored into a common helper between 5.15 and 6.0;
TLB flushing was refactored between 5.4 and 5.10]
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 | 3 +++
mm/mmu_gather.c | 5 +++++
3 files changed, 12 insertions(+)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 268674c1d568..b06240b67199 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -190,12 +190,16 @@ 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 HAVE_RCU_TABLE_FREE
#endif

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

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 55631cd73939..a8f2605cbd0d 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1060,6 +1060,7 @@ 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);
@@ -1407,6 +1408,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
/* step 4: collapse pmd */
_pmd = pmdp_collapse_flush(vma, haddr, pmd);
mm_dec_nr_ptes(mm);
+ tlb_remove_table_sync_one();
pte_free(mm, pmd_pgtable(_pmd));

i_mmap_unlock_write(vma->vm_file->f_mapping);
@@ -1494,6 +1496,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
/* assume page table is clear */
_pmd = pmdp_collapse_flush(vma, addr, pmd);
mm_dec_nr_ptes(mm);
+ tlb_remove_table_sync_one();
pte_free(mm, pmd_pgtable(_pmd));
}
up_write(&mm->mmap_sem);
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 7c1b8f67af7b..341aa036b03c 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -117,6 +117,11 @@ static void tlb_remove_table_smp_sync(void *arg)
/* Simply deliver the interrupt */
}

+void tlb_remove_table_sync_one(void)
+{
+ smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
+}
+
static void tlb_remove_table_one(void *table)
{
/*
--
2.35.1