[PATCH 4.19 20/35] asm-generic/tlb: avoid potential double flush

From: Greg Kroah-Hartman
Date: Mon Jan 04 2021 - 10:59:50 EST


From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit 0758cd8304942292e95a0f750c374533db378b32 upstream.

Aneesh reported that:

tlb_flush_mmu()
tlb_flush_mmu_tlbonly()
tlb_flush() <-- #1
tlb_flush_mmu_free()
tlb_table_flush()
tlb_table_invalidate()
tlb_flush_mmu_tlbonly()
tlb_flush() <-- #2

does two TLBIs when tlb->fullmm, because __tlb_reset_range() will not
clear tlb->end in that case.

Observe that any caller to __tlb_adjust_range() also sets at least one of
the tlb->freed_tables || tlb->cleared_p* bits, and those are
unconditionally cleared by __tlb_reset_range().

Change the condition for actually issuing TLBI to having one of those bits
set, as opposed to having tlb->end != 0.

Link: http://lkml.kernel.org/r/20200116064531.483522-4-aneesh.kumar@xxxxxxxxxxxxx
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.19
Signed-off-by: Santosh Sivaraj <santosh@xxxxxxxxxx>
[santosh: backported to 4.19 stable]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/asm-generic/tlb.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -179,7 +179,12 @@ static inline void __tlb_reset_range(str

static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
{
- if (!tlb->end)
+ /*
+ * Anything calling __tlb_adjust_range() also sets at least one of
+ * these bits.
+ */
+ if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds ||
+ tlb->cleared_puds || tlb->cleared_p4ds))
return;

tlb_flush(tlb);