linux-kernel - Re: [PATCH 3/3] s390/mm: fix mis-accounting of pgtable

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Date:   Wed, 31 Oct 2018 10:39:10 +0100
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Li Wang <liwang@...hat.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Janosch Frank <frankja@...ux.vnet.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 3/3] s390/mm: fix mis-accounting of pgtable_bytes

On Wed, 31 Oct 2018 07:46:47 +0100
Martin Schwidefsky <schwidefsky@...ibm.com> wrote:

> On Wed, 31 Oct 2018 14:43:38 +0800
> Li Wang <liwang@...hat.com> wrote:
> 
> > On Wed, Oct 31, 2018 at 2:31 PM, Martin Schwidefsky <schwidefsky@...ibm.com>
> > wrote:
> >   
> > > BUG: non-zero pgtables_bytes on freeing mm: -16384
> > >    
> > 
> > Okay, the problem is still triggered by LTP/cve-2017-17052.c?  
> 
> No, unfortunately we do not have a simple testcase to trigger this new bug.
> It happened once with one of our test kernels, the path that leads to this
> is completely unclear.
 
Ok, got it. There is a mm_inc_nr_puds(mm) missing in the s390 code:

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 76d89ee8b428..814f26520aa2 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -101,6 +101,7 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
                        mm->context.asce_limit = _REGION1_SIZE;
                        mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
                                _ASCE_USER_BITS | _ASCE_TYPE_REGION2;
+                       mm_inc_nr_puds(mm);
                } else {
                        crst_table_init(table, _REGION1_ENTRY_EMPTY);
                        pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd);

One of our test-cases did an upgrade of a 3-level page table.
I'll update the patch and send a v3.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.