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Fri, 25 Jul 2025 09:22:36 -0700 (PDT) MIME-Version: 1.0 References: <38ed372a-4b27-498e-bb3b-f95792bbbe27@lucifer.local> <9c861191-ac9e-4d26-b2a2-1facfa45de44@redhat.com> In-Reply-To: <9c861191-ac9e-4d26-b2a2-1facfa45de44@redhat.com> From: Jeff Xu Date: Fri, 25 Jul 2025 09:22:23 -0700 X-Gm-Features: Ac12FXzA-vO48FLSIgwm34Yvy9xCrveF7N2ZBWVVo5aGocgvC73fwOsfOIwjfIY Message-ID: Subject: Re: [PATCH v3 2/5] mm/mseal: update madvise() logic To: David Hildenbrand Cc: Lorenzo Stoakes , Andrew Morton , "Liam R . Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kees Cook , linux-hardening@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 5350840005 X-Stat-Signature: 7ibwdcqwnpgbqgrszi3wqcwk111ioyxm X-Rspam-User: X-HE-Tag: 1753460557-993102 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 24, 2025 at 2:53=E2=80=AFPM David Hildenbrand wrote: > > > > >> 4. We could ask applications to switch to non-destructive madvise, > >> like MADV_COLD or MADV_PAGEOUT. Or, another option is that we could > >> switch the kernel to use non-destructive madvise implicitly for > >> destructive madvise in suitable situations. > > > > Umm what? I don't understand your point. > > > >> 5. We could investigate more based on vma->anon_vma > > > > I have no idea what you mean by this. I am an rmap maintainer and have > > worked extensively with anon_vma, what's the point exactly? > > I think, the idea would be to add an additional anon_vma check: so if > you have a MAP_PRIVATE file mapping, you could still allow for > MADV_DONTNEED if you are sure that there are no anon folios in there. > Yes. That is the theory, thanks for clarifying it for me. This is exactly what I was trying to say in my previous response: "We could try having destructive madvise check vma->anon_vma and reject the call if it's true. I haven't had a chance to test this theory yet, though." > If there is an anon_vma, the only way to find out is actually looking at > the page tables. > > To be completely precise, one would have to enlighten the zap logic to > refuse to zap if there is any anon folio there, and bail out. > > -- > Cheers, > > David / dhildenb >