"Verma, Vishal L" <vishal.l.ve...@intel.com> writes:
> On Tue, 2023-12-12 at 08:30 +0800, Huang, Ying wrote:
>> Vishal Verma <vishal.l.ve...@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 <da...@redhat.com>
>> > Cc: Dan Williams <dan.j.willi...@intel.com>
>> > Cc: Dave Jiang <dave.ji...@intel.com>
>> > Cc: Dave Hansen <dave.han...@linux.intel.com>
>> > Cc: Huang Ying <ying.hu...@intel.com>
>> > Tested-by: Li Zhijian <lizhij...@fujitsu.com>
>> > Reviewed-by: Jonathan Cameron <jonathan.came...@huawei.com>
>> > Reviewed-by: David Hildenbrand <da...@redhat.com>
>> > Signed-off-by: Vishal Verma <vishal.l.ve...@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
