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

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Message-Id: <20210104155704.387218698@linuxfoundation.org>
Date:   Mon,  4 Jan 2021 16:57:23 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Santosh Sivaraj <santosh@...six.org>
Subject: [PATCH 4.19 20/35] asm-generic/tlb: avoid potential double flush

From: Peter Zijlstra <peterz@...radead.org>

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@linux.ibm.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc: <stable@...r.kernel.org>  # 4.19
Signed-off-by: Santosh Sivaraj <santosh@...six.org>
[santosh: backported to 4.19 stable]
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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);