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a=openpgp-sha256; l=4012; i=vishal.l.verma@intel.com; h=from:subject:message-id; bh=LlNwsQ9722KaImXgMJUAbGVELQS9Qj5zVBOISdpjDqE=; b=owGbwMvMwCXGf25diOft7jLG02pJDKkbc50VeD8v+CjLFhJhfFzu8RSjtH97erzz9l4Qf8Enc LfQ66hyRykLgxgXg6yYIsvfPR8Zj8ltz+cJTHCEmcPKBDKEgYtTACbiH8TwV1Ju2kePSfLnrhke 2viisS8mpjzc/qGgQObvl8E/GFTs9Rn+B7+fyvC/VG61dh1TyJMbdnVpnpttknc4N2ev5nkgpin HBAA= X-Developer-Key: i=vishal.l.verma@intel.com; a=openpgp; fpr=F8682BE134C67A12332A2ED07AFA61BEA3B84DFF X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1789003572194660413 X-GMAIL-MSGID: 1789003572194660413 Add a sysfs knob for dax devices to control the memmap_on_memory setting if the dax device were to be hotplugged as system memory. The default memmap_on_memory setting for dax devices originating via pmem or hmem is set to 'false' - i.e. no memmap_on_memory semantics, to preserve legacy behavior. For dax devices via CXL, the default is on. The sysfs control allows the administrator to override the above defaults if needed. Cc: David Hildenbrand Cc: Dan Williams Cc: Dave Jiang Cc: Dave Hansen Cc: Huang Ying Tested-by: Li Zhijian Reviewed-by: Jonathan Cameron Reviewed-by: David Hildenbrand Reviewed-by: Huang, Ying Signed-off-by: Vishal Verma Reviewed-by: Alison Schofield --- drivers/dax/bus.c | 43 +++++++++++++++++++++++++++++++++ Documentation/ABI/testing/sysfs-bus-dax | 17 +++++++++++++ 2 files changed, 60 insertions(+) diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c index 0fd948a4443e..27c86d0ca711 100644 --- a/drivers/dax/bus.c +++ b/drivers/dax/bus.c @@ -1349,6 +1349,48 @@ static ssize_t numa_node_show(struct device *dev, } static DEVICE_ATTR_RO(numa_node); +static ssize_t memmap_on_memory_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct dev_dax *dev_dax = to_dev_dax(dev); + + return sysfs_emit(buf, "%d\n", dev_dax->memmap_on_memory); +} + +static ssize_t memmap_on_memory_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t len) +{ + struct dev_dax *dev_dax = to_dev_dax(dev); + bool val; + int rc; + + rc = kstrtobool(buf, &val); + if (rc) + return rc; + + if (val == true && !mhp_supports_memmap_on_memory()) { + dev_dbg(dev, "memmap_on_memory is not available\n"); + return -EOPNOTSUPP; + } + + rc = down_write_killable(&dax_dev_rwsem); + if (rc) + return rc; + + if (dev_dax->memmap_on_memory != val && dev->driver && + to_dax_drv(dev->driver)->type == DAXDRV_KMEM_TYPE) { + up_write(&dax_dev_rwsem); + return -EBUSY; + } + + dev_dax->memmap_on_memory = val; + up_write(&dax_dev_rwsem); + + return len; +} +static DEVICE_ATTR_RW(memmap_on_memory); + static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n) { struct device *dev = container_of(kobj, struct device, kobj); @@ -1375,6 +1417,7 @@ static struct attribute *dev_dax_attributes[] = { &dev_attr_align.attr, &dev_attr_resource.attr, &dev_attr_numa_node.attr, + &dev_attr_memmap_on_memory.attr, NULL, }; diff --git a/Documentation/ABI/testing/sysfs-bus-dax b/Documentation/ABI/testing/sysfs-bus-dax index 6359f7bc9bf4..b34266bfae49 100644 --- a/Documentation/ABI/testing/sysfs-bus-dax +++ b/Documentation/ABI/testing/sysfs-bus-dax @@ -134,3 +134,20 @@ KernelVersion: v5.1 Contact: nvdimm@lists.linux.dev Description: (RO) The id attribute indicates the region id of a dax region. + +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory +Date: January, 2024 +KernelVersion: v6.8 +Contact: nvdimm@lists.linux.dev +Description: + (RW) Control the memmap_on_memory setting if the dax device + were to be hotplugged as system memory. This determines whether + the 'altmap' for the hotplugged memory will be placed on the + device being hotplugged (memmap_on_memory=1) or if it will be + placed on regular memory (memmap_on_memory=0). This attribute + must be set before the device is handed over to the 'kmem' + driver (i.e. hotplugged into system-ram). Additionally, this + depends on CONFIG_MHP_MEMMAP_ON_MEMORY, and a globally enabled + memmap_on_memory parameter for memory_hotplug. This is + typically set on the kernel command line - + memory_hotplug.memmap_on_memory set to 'true' or 'force'."