From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793729972; b=ILcxEsdzNPtJIrhPuyzojbYNkCrXKB/Xr//2DGR3nRhQGBhJ/kQ2//qz24oJRHYOwSrO +h3QO3AOskUvKmYog6oBM8OdQeF0ETMFqB3iBcQzkoOndoGYkWTf5CKAzLfQKf89yDghv biZPaZzlQtfCNc9RKDxngTAhvAF/rbds0U04W64r0S8Yd+Pt0gcYi6SNu0moj3NGScRIr sUeUNt/4dtEGevLkRTyacchl9YT2WjwTsufV7vynjybpvgnv6QuJTMmE3mUofy5Mv9vZA NxPXdn42OcwvY6cPqM4yCrlvN1ke/lFBmY775JSDkVnbIzMzZzpnDkdrOmAxqNzHd8w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793729972; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=ikpjRxzxut3T/KDasjzHggVPTQG5Ge+eGv+OSVemEXk=; b=NDy4V7uz5qpJiOLa/SuEkQNRDiCs5Mkrkz0HzCGJ0XFRHauSwWKK/OwAfaZOxmTnJ7V4 nu9pxlrF62GSHw233B3vb3pYYFNXA6dwdP2wxdusXWOTS8BDndAMvnjrl/bcgxof7+PPU Se+ssru32vW3W5VoJ7hZUiMFMVwOoK2fCwmQGZn5/z4gx7J/l+WhWz9IRqHcX4/X75kY/ Jf2iIYgXGE7pM+hzcun7pCyEdr8S8XM2MLH+C/73W9laYidmAfS58Jlge6ICb7C/lVqoa KzpykTBPV24XTiSbkqnoLw11Cj8H6Hls/5KiXqrITYZgrWUw+nsGxobaXTAsBF/sqbA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=c9sJCu1x; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A960F6082BE7 for ; Tue, 3 Nov 2026 18:19:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=c9sJCu1x Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9D441F00A25; Tue, 3 Nov 2026 18:19:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793729971; bh=ikpjRxzxut3T/KDasjzHggVPTQG5Ge+eGv+OSVemEXk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=c9sJCu1xp74krmFkMVk8mLe2ptw4u+UQIkBrktG1eh45b/H6ID18PQHlk5dcst1r6 gv0yMz7OoYa9jmuiZC4P4il5W4zCsYkIGdBmH+hInR68kATNWaQkYJs/QirwAUbgOW ShcB1cIuQOhXJc28DYjRzkZQJrnE4yyaFMdrNNNTeoo1KNKqyLls8xKxvOE5Si7zd3 cv/GxpIWQPrALyfNuQTqRKlbKITWsNeGtc86ZCTuulJBqnkS/kvuiBlFcuEtZW2SlA 4mhsoIbFCuhL7hyYIjBGvwBuUgSER7Y0n+6fy+dZjsXm4x4DKnHwlRSikzB+wlGYsW O2gdqMVXqF9XA== From: Pratyush Yadav To: Pasha Tatashin , Mike Rapoport , Pratyush Yadav , Andrew Morton , Samiullah Khawaja Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 2/2] mm/memfd_luo: keep memfd frozen until finish Date: Tue, 3 Nov 2026 19:19:14 +0100 Message-ID: <20261103181916.2462825-3-pratyush@kernel.org> X-Mailer: git-send-email 2.56.0.385.gac671c819a-goog In-Reply-To: <20261103181916.2462825-1-pratyush@kernel.org> References: <20261103181916.2462825-1-pratyush@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Pratyush Yadav (Google)" After a memfd is retrieved, it immediately goes back into "normal" operation. The file comes back unfrozen, and its pages can migrate, it can be truncated, and so on. If the memfd is depended on by something, like iommufd, that can open a window for folios to move around before the consumer can re-establish its references. Finish is the conceptual point when a retrieved file can start to behave as "normal". So take an extra reference on the folios and freeze the memfd on retrieve until finish. Suggested-by: Pasha Tatashin Signed-off-by: Pratyush Yadav (Google) --- mm/memfd_luo.c | 87 +++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 68 insertions(+), 19 deletions(-) diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c index 9fd9abf9fedf6..50dbbda47ad3c 100644 --- a/mm/memfd_luo.c +++ b/mm/memfd_luo.c @@ -55,6 +55,14 @@ * Only seals known to this LUO version (see ``MEMFD_LUO_ALL_SEALS``) may * be present; preservation fails with ``-EOPNOTSUPP`` otherwise. * + * Restrictions + * ============ + * + * While a memfd is preserved, and after it is retrieved until the session is + * finished, its size can't be changed and holes can't be punched in it. + * Operations that would do so (``ftruncate()``, ``fallocate()``, writes past + * the end of the file) fail. + * * Non-Preserved Properties * ======================== * @@ -456,33 +464,56 @@ static void memfd_luo_discard_folios(const struct memfd_luo_folio_ser *folios_se } } +/* Drop the references retrieve() holds on the folios added to the file. */ +static void +memfd_luo_put_retrieved_folios(const struct memfd_luo_folio_ser *folios_ser, + u64 nr_folios) +{ + for (u64 i = 0; i < nr_folios; i++) { + const struct memfd_luo_folio_ser *pfolio = &folios_ser[i]; + + if (pfolio->pfn) + folio_put(pfn_folio(pfolio->pfn)); + } +} + static void memfd_luo_finish(struct liveupdate_file_op_args *args) { struct memfd_luo_folio_ser *folios_ser; struct memfd_luo_ser *ser; - /* - * If retrieve was successful, nothing to do. If it failed, retrieve() - * already cleaned up everything it could. So nothing to do there - * either. Only need to clean up when retrieve was not called. - */ - if (args->retrieve_status) + /* If retrieve failed, it already cleaned up everything it could. */ + if (args->retrieve_status < 0) return; ser = phys_to_virt(args->serialized_data); if (!ser) return; - if (ser->nr_folios) { - folios_ser = kho_restore_vmalloc(&ser->folios); - if (!folios_ser) - goto out; + if (args->retrieve_status > 0) { + /* + * Retrieve was successful, release the folios and unfreeze the + * file so it can be used normally. + */ + struct inode *inode = file_inode(args->file); + + folios_ser = args->private_data; + + inode_lock(inode); + memfd_luo_put_retrieved_folios(folios_ser, ser->nr_folios); + shmem_freeze(inode, false); + inode_unlock(inode); - memfd_luo_discard_folios(folios_ser, ser->nr_folios); vfree(folios_ser); + } else if (args->retrieve_status == 0 && ser->nr_folios) { + /* Retrieve was not called, discard the preserved folios. */ + folios_ser = kho_restore_vmalloc(&ser->folios); + if (folios_ser) { + memfd_luo_discard_folios(folios_ser, ser->nr_folios); + vfree(folios_ser); + } } -out: kho_restore_free(ser); } @@ -552,7 +583,10 @@ static int memfd_luo_retrieve_folios(struct file *file, nr_added_pages += npages; folio_add_lru(folio); folio_unlock(folio); - folio_put(folio); + /* + * Keep the reference from kho_restore_folio(). It is dropped + * in finish(). + */ } shmem_recalc_inode(inode, nr_added_pages, 0); @@ -566,9 +600,12 @@ static int memfd_luo_retrieve_folios(struct file *file, folio_put(folio); put_folios: /* - * Note: don't free the folios already added to the file. They will be - * freed when the file is freed. Free the ones not added yet here. + * Drop the references held on the folios already added to the file. + * The folios themselves will be freed when the file is freed. */ + memfd_luo_put_retrieved_folios(folios_ser, i); + + /* Free the ones not added yet here. */ for (long j = i + 1; j < nr_folios; j++) { const struct memfd_luo_folio_ser *pfolio = &folios_ser[j]; phys_addr_t phys; @@ -589,7 +626,7 @@ static int memfd_luo_retrieve_folios(struct file *file, static int memfd_luo_retrieve(struct liveupdate_file_op_args *args) { - struct memfd_luo_folio_ser *folios_ser; + struct memfd_luo_folio_ser *folios_ser = NULL; struct memfd_luo_ser *ser; struct file *file; int err; @@ -624,6 +661,17 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args) vfs_setpos(file, ser->pos, MAX_LFS_FILESIZE); i_size_write(file_inode(file), ser->size); + /* + * Keep the file frozen until finish(). Other preserved objects might + * depend on it. + * + * The file isn't visible to anyone yet, but take the lock anyway since + * shmem_freeze() requires it. + */ + inode_lock(file_inode(file)); + shmem_freeze(file_inode(file), true); + inode_unlock(file_inode(file)); + if (ser->nr_folios) { folios_ser = kho_restore_vmalloc(&ser->folios); if (!folios_ser) { @@ -632,16 +680,17 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args) } err = memfd_luo_retrieve_folios(file, folios_ser, ser->nr_folios); - vfree(folios_ser); if (err) - goto put_file; + goto free_folios_ser; } args->file = file; - kho_restore_free(ser); + args->private_data = folios_ser; return 0; +free_folios_ser: + vfree(folios_ser); put_file: fput(file); free_ser: -- 2.56.0.385.gac671c819a-goog