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@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221128180252.1684965-2-jannh@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221125213714.4115729-2-jannh@xxxxxxxxxx
Fixes: ba76149f47d8 ("thp: khugepaged")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
[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;
TLB flushing was refactored between 4.19 and 5.4;
pmd collapse for PTE-mapped THP was only added in 5.4;
ugly hack needed in <=4.19 for s390]
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
added an incredibly ugly hack to work around the s390 issue reported in
https://lore.kernel.org/all/Y5aaQqNH71IMVks0@sashalap/
include/asm-generic/tlb.h | 6 ++++++
mm/khugepaged.c | 15 +++++++++++++++
mm/memory.c | 5 +++++
3 files changed, 26 insertions(+)
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index db72ad39853b..737f5cb0dc84 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -61,6 +61,12 @@ struct mmu_table_batch {
extern void tlb_table_flush(struct mmu_gather *tlb);
extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
+void tlb_remove_table_sync_one(void);
+
+#else
+
+static inline void tlb_remove_table_sync_one(void) { }
+
#endif
/*
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5dd14ef2e1de..0f217bb9b534 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -23,6 +23,19 @@
#include <asm/pgalloc.h>
#include "internal.h"
+/* gross hack for <=4.19 stable */
+#ifdef CONFIG_S390
+static void tlb_remove_table_smp_sync(void *arg)
+{
+ /* Simply deliver the interrupt */
+}
+
+static void tlb_remove_table_sync_one(void)
+{
+ smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
+}
+#endif
+
enum scan_result {
SCAN_FAIL,
SCAN_SUCCEED,
@@ -1045,6 +1058,7 @@ 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(mm, mmun_start, mmun_end);
+ tlb_remove_table_sync_one();
spin_lock(pte_ptl);
isolated = __collapse_huge_page_isolate(vma, address, pte);
@@ -1294,6 +1308,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
_pmd = pmdp_collapse_flush(vma, addr, pmd);
spin_unlock(ptl);
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/memory.c b/mm/memory.c
index 800834cff4e6..b80ce6b3c8f4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -362,6 +362,11 @@ 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)
{
/*
base-commit: c1ccef20f08e192228a2056808113b453d18c094
--
2.39.0.rc1.256.g54fd8350bd-goog
