diff mbox series

[v3,2/2] dax: add a sysfs knob to control memmap_on_memory behavior

Message ID 20231211-vv-dax_abi-v3-2-acf6cc1bde9f@intel.com
State New
Headers
Series Add DAX ABI for memmap_on_memory |

Commit Message

Verma, Vishal L Dec. 11, 2023, 10:52 p.m. UTC 
  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 <david@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Tested-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 drivers/dax/bus.c                       | 47 +++++++++++++++++++++++++++++++++
 Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
 2 files changed, 64 insertions(+)

Comments

Huang, Ying Dec. 12, 2023, 12:30 a.m. UTC | #1 
Vishal Verma <vishal.l.verma@intel.com> writes:

> 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 <david@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Tested-by: Li Zhijian <lizhijian@fujitsu.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>  drivers/dax/bus.c                       | 47 +++++++++++++++++++++++++++++++++
>  Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
>  2 files changed, 64 insertions(+)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..2871e5188f0d 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1270,6 +1270,52 @@ 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 sprintf(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 device_driver *drv = dev->driver;
> +	struct dev_dax *dev_dax = to_dev_dax(dev);
> +	struct dax_region *dax_region = dev_dax->region;
> +	struct dax_device_driver *dax_drv = to_dax_drv(drv);
> +	ssize_t rc;
> +	bool val;
> +
> +	rc = kstrtobool(buf, &val);
> +	if (rc)
> +		return rc;
> +
> +	if (dev_dax->memmap_on_memory == val)
> +		return len;
> +
> +	device_lock(dax_region->dev);
> +	if (!dax_region->dev->driver) {
> +		device_unlock(dax_region->dev);
> +		return -ENXIO;
> +	}

I think that it should be OK to write to "memmap_on_memory" if no driver
is bound to the device.  We just need to avoid to write to it when kmem
driver is bound.

--
Best Regards,
Huang, Ying

> +
> +	if (dax_drv->type == DAXDRV_KMEM_TYPE) {
> +		device_unlock(dax_region->dev);
> +		return -EBUSY;
> +	}
> +
> +	device_lock(dev);
> +	dev_dax->memmap_on_memory = val;
> +	device_unlock(dev);
> +
> +	device_unlock(dax_region->dev);
> +	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);
> @@ -1296,6 +1342,7 @@ 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 a61a7b186017..b1fd8bf8a7de 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dax
> +++ b/Documentation/ABI/testing/sysfs-bus-dax
> @@ -149,3 +149,20 @@ 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:		October, 2023
> +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'."
Verma, Vishal L Dec. 12, 2023, 12:40 a.m. UTC | #2 
On Tue, 2023-12-12 at 08:30 +0800, Huang, Ying wrote:
> Vishal Verma <vishal.l.verma@intel.com> writes:
> 
> > 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 <david@redhat.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Dave Jiang <dave.jiang@intel.com>
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: Huang Ying <ying.huang@intel.com>
> > Tested-by: Li Zhijian <lizhijian@fujitsu.com>
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Reviewed-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > ---
> >  drivers/dax/bus.c                       | 47 +++++++++++++++++++++++++++++++++
> >  Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
> >  2 files changed, 64 insertions(+)
> > 
> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > index 1ff1ab5fa105..2871e5188f0d 100644
> > --- a/drivers/dax/bus.c
> > +++ b/drivers/dax/bus.c
> > @@ -1270,6 +1270,52 @@ 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 sprintf(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 device_driver *drv = dev->driver;
> > +       struct dev_dax *dev_dax = to_dev_dax(dev);
> > +       struct dax_region *dax_region = dev_dax->region;
> > +       struct dax_device_driver *dax_drv = to_dax_drv(drv);
> > +       ssize_t rc;
> > +       bool val;
> > +
> > +       rc = kstrtobool(buf, &val);
> > +       if (rc)
> > +               return rc;
> > +
> > +       if (dev_dax->memmap_on_memory == val)
> > +               return len;
> > +
> > +       device_lock(dax_region->dev);
> > +       if (!dax_region->dev->driver) {
> > +               device_unlock(dax_region->dev);
> > +               return -ENXIO;
> > +       }
> 
> I think that it should be OK to write to "memmap_on_memory" if no driver
> is bound to the device.  We just need to avoid to write to it when kmem
> driver is bound.

Oh this is just a check on the region driver, not for a dax driver
being bound to the device. It's the same as what things like
align_store(), size_store() etc. do for dax device reconfiguration.

That said, it might be okay to remove this check, as this operation
doesn't change any attributes of the dax region (the other interfaces I
mentioned above can affect regions, so we want to lock the region
device). If removing the check, we'd drop the region lock acquisition
as well.

Dan, any thoughts on this?
Huang, Ying Dec. 12, 2023, 12:56 a.m. UTC | #3 
"Verma, Vishal L" <vishal.l.verma@intel.com> writes:

> On Tue, 2023-12-12 at 08:30 +0800, Huang, Ying wrote:
>> Vishal Verma <vishal.l.verma@intel.com> writes:
>>
>> > 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 <david@redhat.com>
>> > Cc: Dan Williams <dan.j.williams@intel.com>
>> > Cc: Dave Jiang <dave.jiang@intel.com>
>> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> > Cc: Huang Ying <ying.huang@intel.com>
>> > Tested-by: Li Zhijian <lizhijian@fujitsu.com>
>> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>> > Reviewed-by: David Hildenbrand <david@redhat.com>
>> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
>> > ---
>> >  drivers/dax/bus.c                       | 47 +++++++++++++++++++++++++++++++++
>> >  Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
>> >  2 files changed, 64 insertions(+)
>> >
>> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
>> > index 1ff1ab5fa105..2871e5188f0d 100644
>> > --- a/drivers/dax/bus.c
>> > +++ b/drivers/dax/bus.c
>> > @@ -1270,6 +1270,52 @@ 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 sprintf(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 device_driver *drv = dev->driver;
>> > +       struct dev_dax *dev_dax = to_dev_dax(dev);
>> > +       struct dax_region *dax_region = dev_dax->region;
>> > +       struct dax_device_driver *dax_drv = to_dax_drv(drv);
>> > +       ssize_t rc;
>> > +       bool val;
>> > +
>> > +       rc = kstrtobool(buf, &val);
>> > +       if (rc)
>> > +               return rc;
>> > +
>> > +       if (dev_dax->memmap_on_memory == val)
>> > +               return len;
>> > +
>> > +       device_lock(dax_region->dev);
>> > +       if (!dax_region->dev->driver) {
>> > +               device_unlock(dax_region->dev);
>> > +               return -ENXIO;
>> > +       }
>>
>> I think that it should be OK to write to "memmap_on_memory" if no driver
>> is bound to the device.  We just need to avoid to write to it when kmem
>> driver is bound.
>
> Oh this is just a check on the region driver, not for a dax driver
> being bound to the device. It's the same as what things like
> align_store(), size_store() etc. do for dax device reconfiguration.

Sorry, I misunderstood it.

> That said, it might be okay to remove this check, as this operation
> doesn't change any attributes of the dax region (the other interfaces I
> mentioned above can affect regions, so we want to lock the region
> device). If removing the check, we'd drop the region lock acquisition
> as well.

This sounds good to me.

And is it necessary to check driver type with device_lock()?  Can driver
be changed between checking and lock?

--
Best Regards,
Huang, Ying
Dan Williams Dec. 12, 2023, 1 a.m. UTC | #4 
Verma, Vishal L wrote:
> On Tue, 2023-12-12 at 08:30 +0800, Huang, Ying wrote:
> > Vishal Verma <vishal.l.verma@intel.com> writes:
> > 
> > > 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 <david@redhat.com>
> > > Cc: Dan Williams <dan.j.williams@intel.com>
> > > Cc: Dave Jiang <dave.jiang@intel.com>
> > > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > > Cc: Huang Ying <ying.huang@intel.com>
> > > Tested-by: Li Zhijian <lizhijian@fujitsu.com>
> > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > Reviewed-by: David Hildenbrand <david@redhat.com>
> > > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > > ---
> > >  drivers/dax/bus.c                       | 47 +++++++++++++++++++++++++++++++++
> > >  Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
> > >  2 files changed, 64 insertions(+)
> > > 
> > > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > > index 1ff1ab5fa105..2871e5188f0d 100644
> > > --- a/drivers/dax/bus.c
> > > +++ b/drivers/dax/bus.c
> > > @@ -1270,6 +1270,52 @@ 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 sprintf(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 device_driver *drv = dev->driver;
> > > +       struct dev_dax *dev_dax = to_dev_dax(dev);
> > > +       struct dax_region *dax_region = dev_dax->region;
> > > +       struct dax_device_driver *dax_drv = to_dax_drv(drv);
> > > +       ssize_t rc;
> > > +       bool val;
> > > +
> > > +       rc = kstrtobool(buf, &val);
> > > +       if (rc)
> > > +               return rc;
> > > +
> > > +       if (dev_dax->memmap_on_memory == val)
> > > +               return len;
> > > +
> > > +       device_lock(dax_region->dev);
> > > +       if (!dax_region->dev->driver) {
> > > +               device_unlock(dax_region->dev);
> > > +               return -ENXIO;
> > > +       }
> > 
> > I think that it should be OK to write to "memmap_on_memory" if no driver
> > is bound to the device.  We just need to avoid to write to it when kmem
> > driver is bound.
> 
> Oh this is just a check on the region driver, not for a dax driver
> being bound to the device. It's the same as what things like
> align_store(), size_store() etc. do for dax device reconfiguration.
> 
> That said, it might be okay to remove this check, as this operation
> doesn't change any attributes of the dax region (the other interfaces I
> mentioned above can affect regions, so we want to lock the region
> device). If removing the check, we'd drop the region lock acquisition
> as well.
> 
> Dan, any thoughts on this?

Since this is a dev_dax attribute then this would have already been
synchronously shutdown when dax_region->dev->driver transitioned to
NULL. I.e. region unbind causes dev_dax deletion.

However, there's a different issue here as dev->driver was referenced
without the device_lock().

Additionally, I think this function also makes it clear that device lock
flavor of guard() would be useful:

    DEFINE_GUARD(dev, struct device *, device_lock(_T), device_unlock(_T))

...then I would expect something like:

        guard(dev)(dev);
        if (dev_dax->memmap_on_memory != val && dev->driver &&
            to_dax_drv(dev->driver)->type == DAXDRV_KMEM_TYPE)
                return -EBUSY;
        dev_dax->memmap_on_memory = val;
        return len;

...maybe with some temp variables to reduce the derefence chain, buy you
get the idea. Only prevent changes while the device is active under
kmem.
Verma, Vishal L Dec. 12, 2023, 1:02 a.m. UTC | #5 
On Tue, 2023-12-12 at 08:56 +0800, Huang, Ying wrote:
> "Verma, Vishal L" <vishal.l.verma@intel.com> writes:
> 
> > On Tue, 2023-12-12 at 08:30 +0800, Huang, Ying wrote:
> > > 
> > > > +
> > > > +static ssize_t memmap_on_memory_store(struct device *dev,
> > > > +                                     struct device_attribute *attr,
> > > > +                                     const char *buf, size_t len)
> > > > +{
> > > > +       struct device_driver *drv = dev->driver;
> > > > +       struct dev_dax *dev_dax = to_dev_dax(dev);
> > > > +       struct dax_region *dax_region = dev_dax->region;
> > > > +       struct dax_device_driver *dax_drv = to_dax_drv(drv);
> > > > +       ssize_t rc;
> > > > +       bool val;
> > > > +
> > > > +       rc = kstrtobool(buf, &val);
> > > > +       if (rc)
> > > > +               return rc;
> > > > +
> > > > +       if (dev_dax->memmap_on_memory == val)
> > > > +               return len;
> > > > +
> > > > +       device_lock(dax_region->dev);
> > > > +       if (!dax_region->dev->driver) {
> > > > +               device_unlock(dax_region->dev);
> > > > +               return -ENXIO;
> > > > +       }
> > > 
> > > I think that it should be OK to write to "memmap_on_memory" if no driver
> > > is bound to the device.  We just need to avoid to write to it when kmem
> > > driver is bound.
> > 
> > Oh this is just a check on the region driver, not for a dax driver
> > being bound to the device. It's the same as what things like
> > align_store(), size_store() etc. do for dax device reconfiguration.
> 
> Sorry, I misunderstood it.
> 
> > That said, it might be okay to remove this check, as this operation
> > doesn't change any attributes of the dax region (the other interfaces I
> > mentioned above can affect regions, so we want to lock the region
> > device). If removing the check, we'd drop the region lock acquisition
> > as well.
> 
> This sounds good to me.
> 
> And is it necessary to check driver type with device_lock()?  Can driver
> be changed between checking and lock?
> 
Oh, good point, the type check should happen with the device lock held.
I'll make that change.
David Hildenbrand Dec. 12, 2023, 10:05 a.m. UTC | #6 
On 11.12.23 23:52, Vishal Verma wrote:
> 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 <david@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Tested-by: Li Zhijian <lizhijian@fujitsu.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>   drivers/dax/bus.c                       | 47 +++++++++++++++++++++++++++++++++
>   Documentation/ABI/testing/sysfs-bus-dax | 17 ++++++++++++
>   2 files changed, 64 insertions(+)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..2871e5188f0d 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1270,6 +1270,52 @@ 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 sprintf(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 device_driver *drv = dev->driver;
> +	struct dev_dax *dev_dax = to_dev_dax(dev);
> +	struct dax_region *dax_region = dev_dax->region;
> +	struct dax_device_driver *dax_drv = to_dax_drv(drv);
> +	ssize_t rc;
> +	bool val;
> +
> +	rc = kstrtobool(buf, &val);
> +	if (rc)
> +		return rc;
> +
> +	if (dev_dax->memmap_on_memory == val)
> +		return len;
> +
> +	device_lock(dax_region->dev);
> +	if (!dax_region->dev->driver) {
> +		device_unlock(dax_region->dev);
> +		return -ENXIO;
> +	}
> +
> +	if (dax_drv->type == DAXDRV_KMEM_TYPE) {
> +		device_unlock(dax_region->dev);
> +		return -EBUSY;
> +	}
> +
> +	device_lock(dev);
> +	dev_dax->memmap_on_memory = val;
> +	device_unlock(dev);
> +
> +	device_unlock(dax_region->dev);
> +	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);
> @@ -1296,6 +1342,7 @@ 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 a61a7b186017..b1fd8bf8a7de 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dax
> +++ b/Documentation/ABI/testing/sysfs-bus-dax
> @@ -149,3 +149,20 @@ 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:		October, 2023
> +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'."
> 

Thinking about it, I wonder if we could disallow setting that property 
to "true" if the current configuration does not allow it.

That is:

1) Removing the "size" parameter from mhp_supports_memmap_on_memory(), 
it doesn't make any sense anymore.

2) Exporting mhp_supports_memmap_on_memory() to modules.

3) When setting memmap_on_memory, check whether 
mhp_supports_memmap_on_memory() == true.

Then, the user really gets an error when trying to set it to "true".
diff mbox series

Patch

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 1ff1ab5fa105..2871e5188f0d 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -1270,6 +1270,52 @@  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 sprintf(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 device_driver *drv = dev->driver;
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+	struct dax_region *dax_region = dev_dax->region;
+	struct dax_device_driver *dax_drv = to_dax_drv(drv);
+	ssize_t rc;
+	bool val;
+
+	rc = kstrtobool(buf, &val);
+	if (rc)
+		return rc;
+
+	if (dev_dax->memmap_on_memory == val)
+		return len;
+
+	device_lock(dax_region->dev);
+	if (!dax_region->dev->driver) {
+		device_unlock(dax_region->dev);
+		return -ENXIO;
+	}
+
+	if (dax_drv->type == DAXDRV_KMEM_TYPE) {
+		device_unlock(dax_region->dev);
+		return -EBUSY;
+	}
+
+	device_lock(dev);
+	dev_dax->memmap_on_memory = val;
+	device_unlock(dev);
+
+	device_unlock(dax_region->dev);
+	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);
@@ -1296,6 +1342,7 @@  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 a61a7b186017..b1fd8bf8a7de 100644
--- a/Documentation/ABI/testing/sysfs-bus-dax
+++ b/Documentation/ABI/testing/sysfs-bus-dax
@@ -149,3 +149,20 @@  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:		October, 2023
+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'."