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Mon, 19 May 2025 16:02:15 -0700 (PDT) MIME-Version: 1.0 References: <20250519223307.3601786-1-usamaarif642@gmail.com> <20250519223307.3601786-3-usamaarif642@gmail.com> In-Reply-To: <20250519223307.3601786-3-usamaarif642@gmail.com> From: Jann Horn Date: Tue, 20 May 2025 01:01:38 +0200 X-Gm-Features: AX0GCFulMJL6rHKVKOHsAtmVvnT8L9uZ6HQMSQ0zMLUP4ee-O2FJT6ANlZC7bh0 Message-ID: Subject: Re: [PATCH v3 2/7] prctl: introduce PR_DEFAULT_MADV_HUGEPAGE for the process To: Usama Arif , lorenzo.stoakes@oracle.com Cc: Andrew Morton , david@redhat.com, linux-mm@kvack.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, riel@surriel.com, ziy@nvidia.com, laoar.shao@gmail.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, vbabka@suse.cz, Arnd Bergmann , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2D3FB14000B X-Stat-Signature: rngj6bxn5ia9d587oi5b8bb818ty7znu X-Rspam-User: X-HE-Tag: 1747695736-895347 X-HE-Meta: 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 6gSwjxw6 kYsLS+YaM6GgonRjJePqR66RNI75bYlS1ppGef6WjKyDVvLmV2AcezIBdaLEV354WvXxQz4ggS0WK8Qhc7YrLOdqap+sPECVW65Lyotgms9eLq53adLGfm/F787UlNJ8dJ5kma8WmKfRBvPtRQFf3/q3Gv5uNsF8qxKbZuECUjdfX9rSo2GCnQrcKJ2WNSDSIIDDmglOwNZ/jtc6+4O2fSo+BW/5+vOAmaQ6Hak7do7RI38eeZ/gKnjT7bgOqyin1kbNv57/zSim66kM474oB/N0kdvoCM1IK1erI05zxQTdffuwiR7CjZrQP30XONoYasuHZR/PASv7aEp9C3uo6oD7+xkzSfs2w0GGxEKsgpg4uWTA= 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 Tue, May 20, 2025 at 12:33=E2=80=AFAM Usama Arif wrote: > This is set via the new PR_SET_THP_POLICY prctl. It has 2 affects: > - It sets VM_HUGEPAGE and clears VM_NOHUGEPAGE on the default VMA flags > (def_flags). This means that every new VMA will be considered for > hugepage. > - Iterate through every VMA in the process and call hugepage_madvise > on it, with MADV_HUGEPAGE policy. > The policy is inherited during fork+exec. As I replied to Lorenzo's series (https://lore.kernel.org/all/CAG48ez3-7EnBVEjpdoW7z5K0hX41nLQN5Wb65Vg-1p8Dd= XRnjg@mail.gmail.com/), it would be nice if you could avoid introducing new flags that have the combination of all the following properties: 1. persists across exec 2. not cleared on secureexec execution 3. settable without ns_capable(CAP_SYS_ADMIN) 4. settable without NO_NEW_PRIVS Flags that have all of these properties need to be reviewed extra carefully to see if there is any way they could impact the security of setuid binaries, for example by changing mmap() behavior in a way that makes addresses significantly more predictable.