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-rw-r--r--mm/rmap.c36
1 files changed, 36 insertions, 0 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index cd37c1c7e21b..94488b0362f8 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -617,6 +617,13 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm,
tlb_ubc->flush_required = true;
/*
+ * Ensure compiler does not re-order the setting of tlb_flush_batched
+ * before the PTE is cleared.
+ */
+ barrier();
+ mm->tlb_flush_batched = true;
+
+ /*
* If the PTE was dirty then it's best to assume it's writable. The
* caller must use try_to_unmap_flush_dirty() or try_to_unmap_flush()
* before the page is queued for IO.
@@ -643,6 +650,35 @@ static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
return should_defer;
}
+
+/*
+ * Reclaim unmaps pages under the PTL but do not flush the TLB prior to
+ * releasing the PTL if TLB flushes are batched. It's possible for a parallel
+ * operation such as mprotect or munmap to race between reclaim unmapping
+ * the page and flushing the page. If this race occurs, it potentially allows
+ * access to data via a stale TLB entry. Tracking all mm's that have TLB
+ * batching in flight would be expensive during reclaim so instead track
+ * whether TLB batching occurred in the past and if so then do a flush here
+ * if required. This will cost one additional flush per reclaim cycle paid
+ * by the first operation at risk such as mprotect and mumap.
+ *
+ * This must be called under the PTL so that an access to tlb_flush_batched
+ * that is potentially a "reclaim vs mprotect/munmap/etc" race will synchronise
+ * via the PTL.
+ */
+void flush_tlb_batched_pending(struct mm_struct *mm)
+{
+ if (mm->tlb_flush_batched) {
+ flush_tlb_mm(mm);
+
+ /*
+ * Do not allow the compiler to re-order the clearing of
+ * tlb_flush_batched before the tlb is flushed.
+ */
+ barrier();
+ mm->tlb_flush_batched = false;
+ }
+}
#else
static void set_tlb_ubc_flush_pending(struct mm_struct *mm,
struct page *page, bool writable)