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Thu, 22 Jan 2026 10:02:31 -0800 (PST) MIME-Version: 1.0 References: <20260122151842.4069702-1-pratyush@kernel.org> <20260122151842.4069702-3-pratyush@kernel.org> In-Reply-To: <20260122151842.4069702-3-pratyush@kernel.org> From: Pasha Tatashin Date: Thu, 22 Jan 2026 13:01:54 -0500 X-Gm-Features: AZwV_Qg5XreMG7dwNWQ-MFIKK0qTchgxKM2qV59FoSM3HBQMpghysXs5DLe9KBE Message-ID: Subject: Re: [PATCH 2/3] mm: memfd_luo: use memfd_alloc_file() instead of shmem_file_setup() To: Pratyush Yadav Cc: Hugh Dickins , Baolin Wang , Andrew Morton , Mike Rapoport , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 877D040011 X-Stat-Signature: sekn339jo9uez8wow7qpxw3y89w5t4m5 X-HE-Tag: 1769104953-278862 X-HE-Meta: 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 /Tc+7H+F sgcFa4RMhFWWYwBH+N9pz2/ilIJ/MIZXhDw6HYp14ODX+mT8yq9Th/9KHU+KZuJIZ67lY1o7gQl3iiRR+9NZsWW2EvlwkTow158O7EvNC6oJe5wJctMRmA2GXtm76xC+munPf8U4HomO7+eo9YiwTJj2LTmIZFynwQ+wqRWntSSs8QR/bI9weXPy0SWu2i1w4c6FJhUhQeQePpvzHU8pOVpM/GfZ3P3sjAwG6AFs7hmkh5UuSoN2tnNB7gRUodktj11qN8WD1Rn80Dcf0KX+fJos+fQW8JjyP0o9s2z//kH7o4B3dDz0ZOzQ/8nfaxRuo3REucLHIqaaYSZU4GDf2/fju3WjlKFdaUJUIM9yfTYPIdSkdc9elYEcQcjgHYUc0CATcdVAnsSCSghqqjhWebxVESQ== 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, Jan 22, 2026 at 10:19=E2=80=AFAM Pratyush Yadav wrote: > > From: "Pratyush Yadav (Google)" > > When restoring a memfd, the file is created using shmem_file_setup(). > While memfd creation also calls this function to get the file, it also > does other things: > > 1. The O_LARGEFILE flag is set on the file. If this is not done, > writes on the memfd exceeding 2 GiB fail. > > 2. FMODE_LSEEK, FMODE_PREAD, and FMODE_PWRITE are set on the file. > This makes sure the file is seekable and can be used with pread() and > pwrite(). > > 3. Initializes the security field for the inode and makes sure that > inode creation is permitted by the security module. > > Currently, none of those things are done. This means writes above 2 GiB > fail, pread(), and pwrite() fail, and so on. lseek() happens to work > because file_init_path() sets it because shmem defines fop->llseek. > > Fix this by using memfd_alloc_file() to get the file to make sure the > initialization sequence for normal and preserved memfd is the same. > > Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd") > Signed-off-by: Pratyush Yadav (Google) > --- > mm/memfd_luo.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c > index 4f6ba63b4310..01a72e4d3ef6 100644 > --- a/mm/memfd_luo.c > +++ b/mm/memfd_luo.c > @@ -78,6 +78,7 @@ > #include > #include > #include > +#include > #include "internal.h" > > static int memfd_luo_preserve_folios(struct file *file, > @@ -443,8 +444,7 @@ static int memfd_luo_retrieve(struct liveupdate_file_= op_args *args) > if (!ser) > return -EINVAL; > > - file =3D shmem_file_setup("", 0, VM_NORESERVE); > - > + file =3D memfd_alloc_file("", 0); Reviewed-by: Pasha Tatashin