From: Peter Xu <peterx@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Yang Shi <shy828301@gmail.com>, Nadav Amit <nadav.amit@gmail.com>,
David Hildenbrand <david@redhat.com>,
Konstantin Khlebnikov <khlebnikov@openvz.org>
Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent
Date: Fri, 5 Aug 2022 11:52:18 -0400 [thread overview]
Message-ID: <Yu08snXjGZ6V94bp@xz-m1.local> (raw)
In-Reply-To: <20220804154050.e6ab9f8c38e2445acc5b57b1@linux-foundation.org>
On Thu, Aug 04, 2022 at 03:40:50PM -0700, Andrew Morton wrote:
> On Wed, 3 Aug 2022 18:03:29 -0400 Peter Xu <peterx@redhat.com> wrote:
>
> > These bits should only be valid when the ptes are present. Introducing two
> > booleans for it and set it to false when !pte_present().
>
> Please (always) describe the user visible runtime effects of the bug
> which is being fixed?
Will do in the future.
For this specific one I'll add some more details:
The bug is found during code reading and no real world issue reported,
but logically such an error can cause incorrect readings for either smaps
or smaps_rollup output on quite a few fields.
For example, it could cause over-estimate on values like Shared_Dirty,
Private_Dirty, Referenced; or it could also cause under-estimate on
values like LazyFree, Shared_Clean, Private_Clean.
Meanwhile I think I overlooked the pmd handling which seems to have the
same issue but done in another commit.. Will repost soon.
Thanks,
>
>
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> > struct vm_area_struct *vma = walk->vma;
> > bool locked = !!(vma->vm_flags & VM_LOCKED);
> > struct page *page = NULL;
> > - bool migration = false;
> > + bool migration = false, young = false, dirty = false;
> >
> > if (pte_present(*pte)) {
> > page = vm_normal_page(vma, addr, *pte);
> > + young = pte_young(*pte);
> > + dirty = pte_dirty(*pte);
> > } else if (is_swap_pte(*pte)) {
> > swp_entry_t swpent = pte_to_swp_entry(*pte);
> >
> > @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> > if (!page)
> > return;
> >
> > - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> > - locked, migration);
> > + smaps_account(mss, page, false, young, dirty, locked, migration);
> > }
> >
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > --
> > 2.32.0
>
--
Peter Xu
prev parent reply other threads:[~2022-08-05 15:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-03 22:03 [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent Peter Xu
2022-08-04 9:02 ` Vlastimil Babka (SUSE)
2022-08-04 11:01 ` David Hildenbrand
2022-08-04 17:43 ` Yang Shi
2022-08-04 22:40 ` Andrew Morton
2022-08-05 15:52 ` Peter Xu [this message]
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