On Tue, May 17, 2016 at 1:52 AM, Johannes Thumshirn [off-list ref] wrote:

On Sat, May 14, 2016 at 11:26:24PM -0700, Dan Williams wrote:

quoted

Device DAX is the device-centric analogue of Filesystem DAX
(CONFIG_FS_DAX).  It allows memory ranges to be allocated and mapped
without need of an intervening file system.  Device DAX is strict,
precise and predictable.  Specifically this interface:

1/ Guarantees fault granularity with respect to a given page size (pte,
pmd, or pud) set at configuration time.

2/ Enforces deterministic behavior by being strict about what fault
scenarios are supported.

For example, by forcing MADV_DONTFORK semantics and omitting MAP_PRIVATE
support device-dax guarantees that a mapping always behaves/performs the
same once established.  It is the "what you see is what you get" access
mechanism to differentiated memory vs filesystem DAX which has
filesystem specific implementation semantics.

Persistent memory is the first target, but the mechanism is also
targeted for exclusive allocations of performance differentiated memory
ranges.

This commit is limited to the base device driver infrastructure to
associate a dax device with pmem range.

Cc: Jeff Moyer <redacted>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ross Zwisler <redacted>
Signed-off-by: Dan Williams <redacted>
---
 drivers/Kconfig                     |    2
 drivers/Makefile                    |    1
 drivers/dax/Kconfig                 |   25 +++
 drivers/dax/Makefile                |    4 +
 drivers/dax/dax.c                   |  252 +++++++++++++++++++++++++++++++++++
 drivers/dax/dax.h                   |   24 +++
 drivers/dax/pmem.c                  |  168 +++++++++++++++++++++++

Is a DAX device always a NVDIMM device, or can it be something else (like the
S390 dcssblk)? If it's NVDIMM only I'd suggest it to go under the
drivers/nvdimm directory.

The plan is that it can be something else, like high bandwidth memory
for example.

quoted

 tools/testing/nvdimm/Kbuild         |    9 +
 tools/testing/nvdimm/config_check.c |    2
 9 files changed, 487 insertions(+)
 create mode 100644 drivers/dax/Kconfig
 create mode 100644 drivers/dax/Makefile
 create mode 100644 drivers/dax/dax.c
 create mode 100644 drivers/dax/dax.h
 create mode 100644 drivers/dax/pmem.c

diff --git a/drivers/Kconfig b/drivers/Kconfig
index d2ac339de85f..8298eab84a6f 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig

@@ -190,6 +190,8 @@ source "drivers/android/Kconfig"

 source "drivers/nvdimm/Kconfig"

+source "drivers/dax/Kconfig"
+
 source "drivers/nvmem/Kconfig"

 source "drivers/hwtracing/stm/Kconfig"

diff --git a/drivers/Makefile b/drivers/Makefile
index 8f5d076baeb0..0b6f3d60193d 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile

@@ -66,6 +66,7 @@ obj-$(CONFIG_PARPORT)               += parport/
 obj-$(CONFIG_NVM)            += lightnvm/
 obj-y                                += base/ block/ misc/ mfd/ nfc/
 obj-$(CONFIG_LIBNVDIMM)              += nvdimm/
+obj-$(CONFIG_DEV_DAX)                += dax/
 obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf/
 obj-$(CONFIG_NUBUS)          += nubus/
 obj-y                                += macintosh/

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
new file mode 100644
index 000000000000..86ffbaa891ad
--- /dev/null
+++ b/drivers/dax/Kconfig

@@ -0,0 +1,25 @@
+menuconfig DEV_DAX
+     tristate "DAX: direct access to differentiated memory"
+     default m if NVDIMM_DAX
+     help
+       Support raw access to differentiated (persistence, bandwidth,
+       latency...) memory via an mmap(2) capable character
+       device.  Platform firmware or a device driver may identify a
+       platform memory resource that is differentiated from the
+       baseline memory pool.  Mappings of a /dev/daxX.Y device impose
+       restrictions that make the mapping behavior deterministic.
+
+if DEV_DAX
+
+config DEV_DAX_PMEM
+     tristate "PMEM DAX: direct access to persistent memory"
+     depends on NVDIMM_DAX
+     default DEV_DAX
+     help
+       Support raw access to persistent memory.  Note that this
+       driver consumes memory ranges allocated and exported by the
+       libnvdimm sub-system.
+
+       Say Y if unsure
+
+endif

diff --git a/drivers/dax/Makefile b/drivers/dax/Makefile
new file mode 100644
index 000000000000..27c54e38478a
--- /dev/null
+++ b/drivers/dax/Makefile

@@ -0,0 +1,4 @@
+obj-$(CONFIG_DEV_DAX) += dax.o
+obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o
+
+dax_pmem-y := pmem.o

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
new file mode 100644
index 000000000000..8207fb33a992
--- /dev/null
+++ b/drivers/dax/dax.c

[..]

quoted

+void dax_region_put(struct dax_region *dax_region)
+{
+     kref_put(&dax_region->kref, dax_region_free);
+}
+EXPORT_SYMBOL_GPL(dax_region_put);

dax_region_get() ??

There's currently no public (outside of dax.c) usage for taking a
reference against a region.  This export is really only there to keep
dax_region_free() private.

quoted

+
+static void dax_dev_free(struct kref *kref)
+{
+     struct dax_dev *dax_dev;
+
+     dax_dev = container_of(kref, struct dax_dev, kref);
+     dax_region_put(dax_dev->region);
+     kfree(dax_dev);
+}
+
+static void dax_dev_put(struct dax_dev *dax_dev)
+{
+     kref_put(&dax_dev->kref, dax_dev_free);
+}
+
+struct dax_region *alloc_dax_region(struct device *parent, int region_id,
+             struct resource *res, unsigned int align, void *addr,
+             unsigned long pfn_flags)
+{
+     struct dax_region *dax_region;
+
+     dax_region = kzalloc(sizeof(*dax_region), GFP_KERNEL);
+
+     if (!dax_region)
+             return NULL;
+
+     memcpy(&dax_region->res, res, sizeof(*res));
+     dax_region->pfn_flags = pfn_flags;
+     kref_init(&dax_region->kref);
+     dax_region->id = region_id;
+     ida_init(&dax_region->ida);
+     dax_region->align = align;
+     dax_region->dev = parent;
+     dax_region->base = addr;
+
+     return dax_region;
+}
+EXPORT_SYMBOL_GPL(alloc_dax_region);
+
+static ssize_t size_show(struct device *dev,
+             struct device_attribute *attr, char *buf)
+{
+     struct dax_dev *dax_dev = dev_get_drvdata(dev);
+     unsigned long long size = 0;
+     int i;
+
+     for (i = 0; i < dax_dev->num_resources; i++)
+             size += resource_size(&dax_dev->res[i]);
+
+     return sprintf(buf, "%llu\n", size);
+}
+static DEVICE_ATTR_RO(size);
+
+static struct attribute *dax_device_attributes[] = {
+     &dev_attr_size.attr,
+     NULL,
+};
+
+static const struct attribute_group dax_device_attribute_group = {
+     .attrs = dax_device_attributes,
+};
+
+static const struct attribute_group *dax_attribute_groups[] = {
+     &dax_device_attribute_group,
+     NULL,
+};
+
+static void destroy_dax_dev(void *_dev)
+{
+     struct device *dev = _dev;
+     struct dax_dev *dax_dev = dev_get_drvdata(dev);
+     struct dax_region *dax_region = dax_dev->region;
+
+     dev_dbg(dev, "%s\n", __func__);

This dev_dbg() could be replaced by function graph tracing.

Not without an explicit trace point to re-add the dev_printk details.
What I really want, and has been on the back burner for a long time,
is to enhance dynamic debug to turn all individual dev_dbg()
statements optionally into trace points.

quoted

+
+     get_device(dev);
+     device_unregister(dev);
+     ida_simple_remove(&dax_region->ida, dax_dev->id);
+     ida_simple_remove(&dax_minor_ida, MINOR(dev->devt));
+     put_device(dev);
+     dax_dev_put(dax_dev);
+}
+
+int devm_create_dax_dev(struct dax_region *dax_region, struct resource *res,
+             int count)
+{
+     struct device *parent = dax_region->dev;
+     struct dax_dev *dax_dev;
+     struct device *dev;
+     int rc, minor;
+     dev_t dev_t;
+
+     dax_dev = kzalloc(sizeof(*dax_dev) + sizeof(*res) * count, GFP_KERNEL);
+     if (!dax_dev)
+             return -ENOMEM;
+     memcpy(dax_dev->res, res, sizeof(*res) * count);
+     dax_dev->num_resources = count;
+     kref_init(&dax_dev->kref);
+     dax_dev->region = dax_region;
+     kref_get(&dax_region->kref);

dax_region_get() ?

I'm not sure that trivial wrapper is worth it.

quoted

+
+     dax_dev->id = ida_simple_get(&dax_region->ida, 0, 0, GFP_KERNEL);
+     if (dax_dev->id < 0) {
+             rc = dax_dev->id;
+             goto err_id;
+     }
+
+     minor = ida_simple_get(&dax_minor_ida, 0, 0, GFP_KERNEL);
+     if (minor < 0) {
+             rc = minor;
+             goto err_minor;
+     }
+
+     dev_t = MKDEV(dax_major, minor);
+     dev = device_create_with_groups(dax_class, parent, dev_t, dax_dev,
+                     dax_attribute_groups, "dax%d.%d", dax_region->id,
+                     dax_dev->id);
+     if (IS_ERR(dev)) {
+             rc = PTR_ERR(dev);
+             goto err_create;
+     }
+     dax_dev->dev = dev;
+
+     rc = devm_add_action(dax_region->dev, destroy_dax_dev, dev);
+     if (rc) {
+             destroy_dax_dev(dev);
+             return rc;
+     }
+
+     return 0;
+
+ err_create:
+     ida_simple_remove(&dax_minor_ida, minor);
+ err_minor:
+     ida_simple_remove(&dax_region->ida, dax_dev->id);
+ err_id:
+     dax_dev_put(dax_dev);
+
+     return rc;
+}
+EXPORT_SYMBOL_GPL(devm_create_dax_dev);
+
+static const struct file_operations dax_fops = {
+     .llseek = noop_llseek,
+     .owner = THIS_MODULE,
+};
+
+static int __init dax_init(void)
+{
+     int rc;
+
+     rc = register_chrdev(0, "dax", &dax_fops);
+     if (rc < 0)
+             return rc;
+     dax_major = rc;
+
+     dax_class = class_create(THIS_MODULE, "dax");
+     if (IS_ERR(dax_class)) {
+             unregister_chrdev(dax_major, "dax");
+             return PTR_ERR(dax_class);
+     }
+
+     return 0;
+}
+
+static void __exit dax_exit(void)
+{
+     class_destroy(dax_class);
+     unregister_chrdev(dax_major, "dax");

AFAICT you're missing a call to ida_destroy(&dax_minor_ida); here.

Indeed, you're right.  That same bug is also present in multiple
places in drivers/nvdimm/.

[..]

quoted

diff --git a/drivers/dax/dax.h b/drivers/dax/dax.h
new file mode 100644
index 000000000000..d8b8f1f25054
--- /dev/null
+++ b/drivers/dax/dax.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright(c) 2016 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#ifndef __DAX_H__
+#define __DAX_H__
+struct device;
+struct resource;
+struct dax_region;
+void dax_region_put(struct dax_region *dax_region);
+struct dax_region *alloc_dax_region(struct device *parent,
+             int region_id, struct resource *res, unsigned int align,
+             void *addr, unsigned long flags);
+int devm_create_dax_dev(struct dax_region *dax_region, struct resource *res,
+             int count);
+#endif /* __DAX_H__ */

diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
new file mode 100644
index 000000000000..4e97555e1cab
--- /dev/null
+++ b/drivers/dax/pmem.c

@@ -0,0 +1,168 @@
+/*
+ * Copyright(c) 2016 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/percpu-refcount.h>
+#include <linux/memremap.h>
+#include <linux/module.h>
+#include <linux/pfn_t.h>
+#include "../nvdimm/pfn.h"
+#include "../nvdimm/nd.h"
+#include "dax.h"
+
+struct dax_pmem {
+     struct device *dev;
+     struct percpu_ref ref;
+     struct completion cmp;
+};
+
+struct dax_pmem *to_dax_pmem(struct percpu_ref *ref)
+{
+     return container_of(ref, struct dax_pmem, ref);
+}
+
+static void dax_pmem_percpu_release(struct percpu_ref *ref)
+{
+     struct dax_pmem *dax_pmem = to_dax_pmem(ref);
+
+     dev_dbg(dax_pmem->dev, "%s\n", __func__);

This dev_dbg() could be replaced by function graph tracing.

[..]

quoted

+     dev_dbg(dax_pmem->dev, "%s\n", __func__);

Same as above.

[..]

quoted

+     dev_dbg(dax_pmem->dev, "%s\n", __func__);

Same as above.

Same reply as before to these...

quoted

+     percpu_ref_kill(ref);
+}
+
+static int dax_pmem_probe(struct device *dev)
+{
+     int rc;
+     void *addr;
+     struct resource res;
+     struct nd_pfn_sb *pfn_sb;
+     struct dax_pmem *dax_pmem;
+     struct nd_region *nd_region;
+     struct nd_namespace_io *nsio;
+     struct dax_region *dax_region;
+     struct nd_namespace_common *ndns;
+     struct nd_dax *nd_dax = to_nd_dax(dev);
+     struct nd_pfn *nd_pfn = &nd_dax->nd_pfn;
+     struct vmem_altmap __altmap, *altmap = NULL;
+
+     ndns = nvdimm_namespace_common_probe(dev);
+     if (IS_ERR(ndns))
+             return PTR_ERR(ndns);
+     nsio = to_nd_namespace_io(&ndns->dev);
+
+     /* parse the 'pfn' info block via ->rw_bytes */
+     devm_nsio_enable(dev, nsio);
+     altmap = nvdimm_setup_pfn(nd_pfn, &res, &__altmap);
+     if (IS_ERR(altmap))
+             return PTR_ERR(altmap);
+     devm_nsio_disable(dev, nsio);
+
+     pfn_sb = nd_pfn->pfn_sb;
+
+     if (!devm_request_mem_region(dev, nsio->res.start,
+                             resource_size(&nsio->res), dev_name(dev))) {
+             dev_warn(dev, "could not reserve region %pR\n", &nsio->res);
+             return -EBUSY;
+     }
+
+     dax_pmem = devm_kzalloc(dev, sizeof(*dax_pmem), GFP_KERNEL);
+     if (!dax_pmem)
+             return -ENOMEM;
+
+     dax_pmem->dev = dev;
+     init_completion(&dax_pmem->cmp);
+     rc = percpu_ref_init(&dax_pmem->ref, dax_pmem_percpu_release, 0,
+                     GFP_KERNEL);
+     if (rc)
+             return rc;
+
+     rc = devm_add_action(dev, dax_pmem_percpu_exit, &dax_pmem->ref);
+     if (rc) {
+             dax_pmem_percpu_exit(&dax_pmem->ref);
+             return rc;
+     }
+
+     addr = devm_memremap_pages(dev, &res, &dax_pmem->ref, altmap);
+     if (IS_ERR(addr))
+             return PTR_ERR(addr);
+
+     rc = devm_add_action(dev, dax_pmem_percpu_kill, &dax_pmem->ref);
+     if (rc) {
+             dax_pmem_percpu_kill(&dax_pmem->ref);
+             return rc;
+     }
+
+     nd_region = to_nd_region(dev->parent);
+     dax_region = alloc_dax_region(dev, nd_region->id, &res,
+                     le32_to_cpu(pfn_sb->align), addr, PFN_DEV|PFN_MAP);
+     if (!dax_region)
+             return -ENOMEM;
+
+     /* TODO: support for subdividing a dax region... */
+     rc = devm_create_dax_dev(dax_region, &res, 1);
+
+     /* child dax_dev instances now own the lifetime of the dax_region */
+     dax_region_put(dax_region);
+
+     return rc;
+}
+
+static int dax_pmem_remove(struct device *dev)
+{
+     /*
+      * The init path is fully devm-enabled, or child devices
+      * otherwise hold references on parent resources.
+      */

So remove is completely pointless here. Why are you depending on it in
__nd_driver_register()? __device_release_driver() does not depend on a remove
callback to be present.

Good point, I'll just remove the need for it.

[..]

Thanks, Johannes!