[RFC 14/20] mm: move inc/dec_tlb_flush_pending() to mmu_gather.c

Nadav Amit
2021-01-31T00:19:28Z

From: Nadav Amit <namit@vmware.com>

Reduce the chances that inc/dec_tlb_flush_pending() will be abused by
moving them into mmu_gather.c, which is more of their natural place.
This also allows to reduce the clutter on mm_types.h.

Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: x86@kernel.org
---
include/linux/mm_types.h | 54 ----------------------------------------
mm/mmu_gather.c | 54 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+), 54 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 812ee0fd4c35..676795dfd5d4 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -615,60 +615,6 @@ static inline void init_tlb_flush_pending(struct mm_struct *mm)
atomic_set(&mm->tlb_flush_pending, 0);
}

-static inline void inc_tlb_flush_pending(struct mm_struct *mm)
-{
- atomic_inc(&mm->tlb_flush_pending);
- /*
- * The only time this value is relevant is when there are indeed pages
- * to flush. And we'll only flush pages after changing them, which
- * requires the PTL.
- *
- * So the ordering here is:
- *
- * atomic_inc(&mm->tlb_flush_pending);
- * spin_lock(&ptl);
- * ...
- * set_pte_at();
- * spin_unlock(&ptl);
- *
- * spin_lock(&ptl)
- * mm_tlb_flush_pending();
- * ....
- * spin_unlock(&ptl);
- *
- * flush_tlb_range();
- * atomic_dec(&mm->tlb_flush_pending);
- *
- * Where the increment if constrained by the PTL unlock, it thus
- * ensures that the increment is visible if the PTE modification is
- * visible. After all, if there is no PTE modification, nobody cares
- * about TLB flushes either.
- *
- * This very much relies on users (mm_tlb_flush_pending() and
- * mm_tlb_flush_nested()) only caring about _specific_ PTEs (and
- * therefore specific PTLs), because with SPLIT_PTE_PTLOCKS and RCpc
- * locks (PPC) the unlock of one doesn't order against the lock of
- * another PTL.
- *
- * The decrement is ordered by the flush_tlb_range(), such that
- * mm_tlb_flush_pending() will not return false unless all flushes have
- * completed.
- */
-}
-
-static inline void dec_tlb_flush_pending(struct mm_struct *mm)
-{
- /*
- * See inc_tlb_flush_pending().
- *
- * This cannot be smp_mb__before_atomic() because smp_mb() simply does
- * not order against TLB invalidate completion, which is what we need.
- *
- * Therefore we must rely on tlb_flush_*() to guarantee order.
- */
- atomic_dec(&mm->tlb_flush_pending);
-}
-
static inline bool mm_tlb_flush_pending(struct mm_struct *mm)
{
/*
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 5a659d4e59eb..13338c096cc6 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -249,6 +249,60 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
tlb_flush_mmu_free(tlb);
}

+static inline void inc_tlb_flush_pending(struct mm_struct *mm)
+{
+ atomic_inc(&mm->tlb_flush_pending);
+ /*
+ * The only time this value is relevant is when there are indeed pages
+ * to flush. And we'll only flush pages after changing them, which
+ * requires the PTL.
+ *
+ * So the ordering here is:
+ *
+ * atomic_inc(&mm->tlb_flush_pending);
+ * spin_lock(&ptl);
+ * ...
+ * set_pte_at();
+ * spin_unlock(&ptl);
+ *
+ * spin_lock(&ptl)
+ * mm_tlb_flush_pending();
+ * ....
+ * spin_unlock(&ptl);
+ *
+ * flush_tlb_range();
+ * atomic_dec(&mm->tlb_flush_pending);
+ *
+ * Where the increment if constrained by the PTL unlock, it thus
+ * ensures that the increment is visible if the PTE modification is
+ * visible. After all, if there is no PTE modification, nobody cares
+ * about TLB flushes either.
+ *
+ * This very much relies on users (mm_tlb_flush_pending() and
+ * mm_tlb_flush_nested()) only caring about _specific_ PTEs (and
+ * therefore specific PTLs), because with SPLIT_PTE_PTLOCKS and RCpc
+ * locks (PPC) the unlock of one doesn't order against the lock of
+ * another PTL.
+ *
+ * The decrement is ordered by the flush_tlb_range(), such that
+ * mm_tlb_flush_pending() will not return false unless all flushes have
+ * completed.
+ */
+}
+
+static inline void dec_tlb_flush_pending(struct mm_struct *mm)
+{
+ /*
+ * See inc_tlb_flush_pending().
+ *
+ * This cannot be smp_mb__before_atomic() because smp_mb() simply does
+ * not order against TLB invalidate completion, which is what we need.
+ *
+ * Therefore we must rely on tlb_flush_*() to guarantee order.
+ */
+ atomic_dec(&mm->tlb_flush_pending);
+}
+
/**
* tlb_gather_mmu - initialize an mmu_gather structure for page-table tear-down
* @tlb: the mmu_gather structure to initialize
--
2.25.1