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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-50148ee050esm26853761cf.30.2026.01.14.18.42.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Jan 2026 18:42:59 -0800 (PST) From: Gregory Price To: linux-mm@kvack.org Cc: linux-cxl@vger.kernel.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, kernel-team@meta.com, dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, david@kernel.org, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, osalvador@suse.de, akpm@linux-foundation.org Subject: [PATCH] dax/kmem: add build config for protected dax memory blocks Date: Wed, 14 Jan 2026 21:42:22 -0500 Message-ID: <20260115024222.3486455-1-gourry@gourry.net> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260114235022.3437787-6-gourry@gourry.net> References: <20260114235022.3437787-6-gourry@gourry.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E4B4A180005 X-Stat-Signature: bkguriait1hjufw9nunne7y6wtbxuaqx X-HE-Tag: 1768444980-33750 X-HE-Meta: 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 E4c/pbUl sLmN8yWGn8G4wkXlrUUFywJEafLyPHJCcxSAGBjDXmnCxF+8tNrh2f53bG3ya474Z+jbup0KSrSslRy3C1zMTtSzc4vfSXln1ots2OGHlfmfkHs3o3BXVcPgpKgV3SlTs/HiIImnktHCDWoMJYHVJJnmx8+T3W7uVtugSzkJOwY6fTqlx9R60ESbBDQGgIV6oxuce7tqAJ8cJcHlbPF2qBq/ucw/kChfOnKDzWSFdKdwktd+4lJTYVUdpiajcvPnLI8JyE0NlmgHzxeFoLP6HfE2NgPWJeAaksl6jZ5X/qgRXYiRnB6U4t5cxPAMmdRqiG9KELh3cVO9TzEQ= 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: Since this protection may break userspace tools, it should be an opt-in until those tools have time to update to the new daxN.M/hotplug interface instead of memory blocks. Suggested-by: Dan Williams Signed-off-by: Gregory Price --- drivers/dax/Kconfig | 18 ++++++++++++++++++ drivers/dax/kmem.c | 29 ++++++++++++++++++++--------- 2 files changed, 38 insertions(+), 9 deletions(-) diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig index d656e4c0eb84..cc13c22eb8f8 100644 --- a/drivers/dax/Kconfig +++ b/drivers/dax/Kconfig @@ -78,4 +78,22 @@ config DEV_DAX_KMEM Say N if unsure. +config DEV_DAX_KMEM_PROTECTED + bool "Protect DAX_KMEM memory blocks being changed" + depends on DEV_DAX_KMEM + default n + help + Prevents actions from outside the KMEM DAX driver from changing + DAX KMEM memory block states. For example, the memory block + sysfs functions (online, state) will return -EBUSY, and normal + calls to memory_hotplug functions from other drivers and kernel + sources will fail. + + This may break existing memory block management patterns that + depend on offlining DAX KMEM blocks from userland before unbinding + the driver. Use this only if your tools have been updated to use + the daxN.M/hotplug interface. + + Say N if unsure. + endif diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c index f3562f65376c..094b8a51099e 100644 --- a/drivers/dax/kmem.c +++ b/drivers/dax/kmem.c @@ -184,6 +184,21 @@ static int dax_kmem_memory_notifier_cb(struct notifier_block *nb, return NOTIFY_BAD; } +static int dax_kmem_register_notifier(struct dax_kmem_data *data) +{ + if (!IS_ENABLED(DEV_DAX_KMEM_PROTECTED)) + return 0; + data->mem_nb.notifier_call = dax_kmem_memory_notifier_cb; + return register_memory_notifier(&data->mem_nb); +} + +static void dax_kmem_unregister_notifier(struct dax_kmem_data *data) +{ + if (!IS_ENABLED(DEV_DAX_KMEM_PROTECTED)) + return; + unregister_memory_notifier(&data->mem_nb); +} + /** * dax_kmem_do_hotplug - hotplug memory for dax kmem device * @dev_dax: the dev_dax instance @@ -563,13 +578,9 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax) if (rc < 0) goto err_resources; - /* Register memory notifier to block external operations */ - data->mem_nb.notifier_call = dax_kmem_memory_notifier_cb; - rc = register_memory_notifier(&data->mem_nb); - if (rc) { - dev_warn(dev, "failed to register memory notifier\n"); + rc = dax_kmem_register_notifier(data); + if (rc) goto err_notifier; - } /* * Hotplug using the system default policy - this preserves backwards @@ -595,7 +606,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax) return 0; err_hotplug: - unregister_memory_notifier(&data->mem_nb); + dax_kmem_unregister_notifier(data); err_notifier: dax_kmem_cleanup_resources(dev_dax, data); err_resources: @@ -619,7 +630,7 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax) device_remove_file(dev, &dev_attr_hotplug); dax_kmem_cleanup_resources(dev_dax, data); - unregister_memory_notifier(&data->mem_nb); + dax_kmem_unregister_notifier(data); memory_group_unregister(data->mgid); kfree(data->res_name); kfree(data); @@ -640,7 +651,7 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax) struct dax_kmem_data *data = dev_get_drvdata(dev); device_remove_file(dev, &dev_attr_hotplug); - unregister_memory_notifier(&data->mem_nb); + dax_kmem_unregister_notifier(data); /* * Without hotremove purposely leak the request_mem_region() for the -- 2.52.0