linux-kernel - Re: [PATCH RFC] mm: userfaultfd: correct dirty flags set for both present and swap pte

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Message-ID: <CAJuCfpF39YCc_aC1qnSHxmn8QwT+BB+OSHUJqGHn_ABoS9pBeg@mail.gmail.com>
Date: Thu, 8 May 2025 08:33:08 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Peter Xu <peterx@...hat.com>
Cc: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>, 
	David Hildenbrand <david@...hat.com>, Lokesh Gidra <lokeshgidra@...gle.com>
Subject: Re: [PATCH RFC] mm: userfaultfd: correct dirty flags set for both
 present and swap pte

On Thu, May 8, 2025 at 8:23 AM Peter Xu <peterx@...hat.com> wrote:
>
> On Thu, May 08, 2025 at 09:07:35PM +1200, Barry Song wrote:
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > As David pointed out, what truly matters for mremap and userfaultfd
> > move operations is the soft dirty bit. The current comment and
> > implementation—which always sets the dirty bit for present PTEs
> > and fails to set the soft dirty bit for swap PTEs—are incorrect.
> > This patch updates the behavior to correctly set the soft dirty bit
> > for both present and swap PTEs in accordance with mremap.
> >
> > Reported-by: David Hildenbrand <david@...hat.com>
> > Closes: https://lore.kernel.org/linux-mm/02f14ee1-923f-47e3-a994-4950afb9afcc@redhat.com/
> > Cc: Peter Xu <peterx@...hat.com>
> > Cc: Suren Baghdasaryan <surenb@...gle.com>
> > Cc: Lokesh Gidra <lokeshgidra@...gle.com>
> > Signed-off-by: Barry Song <v-songbaohua@...o.com>
>
> Acked-by: Peter Xu <peterx@...hat.com>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

The function was introduced in 6.8. We should probably CC stable as well.

>
> --
> Peter Xu
>