Patch "mm,thp: khugepaged: call pte flush at the time of collapse" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm,thp: khugepaged: call pte flush at the time of collapse

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-thp-khugepaged-call-pte-flush-at-the-time-of-collapse.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 6a6ac72fd6ea32594b316513e1826c3f6db4cc93 Mon Sep 17 00:00:00 2001
From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Date: Thu, 11 Feb 2016 16:13:09 -0800
Subject: mm,thp: khugepaged: call pte flush at the time of collapse

From: Vineet Gupta <Vineet.Gupta1@synopsys.com>

commit 6a6ac72fd6ea32594b316513e1826c3f6db4cc93 upstream.

This showed up on ARC when running LMBench bw_mem tests as Overlapping
TLB Machine Check Exception triggered due to STLB entry (2M pages)
overlapping some NTLB entry (regular 8K page).

bw_mem 2m touches a large chunk of vaddr creating NTLB entries.  In the
interim khugepaged kicks in, collapsing the contiguous ptes into a
single pmd.  pmdp_collapse_flush()->flush_pmd_tlb_range() is called to
flush out NTLB entries for the ptes.  This for ARC (by design) can only
shootdown STLB entries (for pmd).  The stray NTLB entries cause the
overlap with the subsequent STLB entry for collapsed page.  So make
pmdp_collapse_flush() call pte flush interface not pmd flush.

Note that originally all thp flush call sites in generic code called
flush_tlb_range() leaving it to architecture to implement the flush for
pte and/or pmd.  Commit 12ebc1581ad11454 changed this by calling a new
opt-in API flush_pmd_tlb_range() which made the semantics more explicit
but failed to distinguish the pte vs pmd flush in generic code, which is
what this patch fixes.

Note that ARC can fixed w/o touching the generic pmdp_collapse_flush()
by defining a ARC version, but that defeats the purpose of generic
version, plus sementically this is the right thing to do.

Fixes STAR 9000961194: LMBench on AXS103 triggering duplicate TLB
exceptions with super pages

Fixes: 12ebc1581ad11454 ("mm,thp: introduce flush_pmd_tlb_range")
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/pgtable-generic.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -210,7 +210,9 @@ pmd_t pmdp_collapse_flush(struct vm_area
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	VM_BUG_ON(pmd_trans_huge(*pmdp));
 	pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
-	flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
+
+	/* collapse entails shooting down ptes not pmd */
+	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 	return pmd;
 }
 #endif


Patches currently in stable-queue which might be from Vineet.Gupta1@synopsys.com are

queue-4.4/mm-thp-khugepaged-call-pte-flush-at-the-time-of-collapse.patch