[Devel] [PATCH RHEL8 COMMIT] ms/asm-generic/tlb: avoid potential double flush

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.47
------>
commit 64a9ad9aafb23bba3186ee96dc51c9cca65806ed
Author: Peter Zijlstra <peterz at infradead.org>
Date:   Mon Jun 21 20:01:20 2021 +0300

    ms/asm-generic/tlb: avoid potential double flush
    
    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 at infradead.org>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
    Reported-by: "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com>
    Cc: Michael Ellerman <mpe at ellerman.id.au>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-101300
    (cherry picked from ms commit 0758cd8304942292e95a0f750c374533db378b32)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    
    (cherry picked from vz7 commit f64be64b0e3d460cd44eef5371e2142e8099bdc4)
    https://jira.sw.ru/browse/PSBM-127854
    Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
---
 include/asm-generic/tlb.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 43c4aca1a6b8..af766d2b4761 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -193,7 +193,12 @@ static inline unsigned long tlb_get_unmap_size(struct mmu_gather *tlb)
 
 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);