Re: [PATCH v4 14/21] cxl/mbox: Add exclusive kernel command support

[Ben Widawsky <ben.widawsky@intel.com>]

On 21-09-08 22:12:49, Dan Williams wrote:
> The CXL_PMEM driver expects exclusive control of the label storage area
> space. Similar to the LIBNVDIMM expectation that the label storage area
> is only writable from userspace when the corresponding memory device is
> not active in any region, the expectation is the native CXL_PCI UAPI
> path is disabled while the cxl_nvdimm for a given cxl_memdev device is
> active in LIBNVDIMM.
> 
> Add the ability to toggle the availability of a given command for the
> UAPI path. Use that new capability to shutdown changes to partitions and
> the label storage area while the cxl_nvdimm device is actively proxying
> commands for LIBNVDIMM.
> 
> Acked-by: Ben Widawsky <ben.widawsky@intel.com>
> Link: https://lore.kernel.org/r/162982123298.1124374.22718002900700392.stgit@dwillia2-desk3.amr.corp.intel.com
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

I really wanted a way to make the exclusivity a property of the command itself
and determine whether or not there's an nvdimm bridge connected before
dispatching the command. Unfortunately, I couldn't make anything that was less
complex than this, so it is upgraded to:
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>

> ---
>  drivers/cxl/core/mbox.c   |    5 +++++
>  drivers/cxl/core/memdev.c |   31 +++++++++++++++++++++++++++++++
>  drivers/cxl/cxlmem.h      |    4 ++++
>  drivers/cxl/pmem.c        |   43 ++++++++++++++++++++++++++++++++-----------
>  4 files changed, 72 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 422999740649..82e79da195fa 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -221,6 +221,7 @@ static bool cxl_mem_raw_command_allowed(u16 opcode)
>   *  * %-EINVAL	- Reserved fields or invalid values were used.
>   *  * %-ENOMEM	- Input or output buffer wasn't sized properly.
>   *  * %-EPERM	- Attempted to use a protected command.
> + *  * %-EBUSY	- Kernel has claimed exclusive access to this opcode
>   *
>   * The result of this command is a fully validated command in @out_cmd that is
>   * safe to send to the hardware.
> @@ -296,6 +297,10 @@ static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,
>  	if (!test_bit(info->id, cxlm->enabled_cmds))
>  		return -ENOTTY;
>  
> +	/* Check that the command is not claimed for exclusive kernel use */
> +	if (test_bit(info->id, cxlm->exclusive_cmds))
> +		return -EBUSY;
> +
>  	/* Check the input buffer is the expected size */
>  	if (info->size_in >= 0 && info->size_in != send_cmd->in.size)
>  		return -ENOMEM;
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index df2ba87238c2..d9ade5b92330 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -134,6 +134,37 @@ static const struct device_type cxl_memdev_type = {
>  	.groups = cxl_memdev_attribute_groups,
>  };
>  
> +/**
> + * set_exclusive_cxl_commands() - atomically disable user cxl commands
> + * @cxlm: cxl_mem instance to modify
> + * @cmds: bitmap of commands to mark exclusive
> + *
> + * Flush the ioctl path and disable future execution of commands with
> + * the command ids set in @cmds.
> + */
> +void set_exclusive_cxl_commands(struct cxl_mem *cxlm, unsigned long *cmds)
> +{
> +	down_write(&cxl_memdev_rwsem);
> +	bitmap_or(cxlm->exclusive_cmds, cxlm->exclusive_cmds, cmds,
> +		  CXL_MEM_COMMAND_ID_MAX);
> +	up_write(&cxl_memdev_rwsem);
> +}
> +EXPORT_SYMBOL_GPL(set_exclusive_cxl_commands);
> +
> +/**
> + * clear_exclusive_cxl_commands() - atomically enable user cxl commands
> + * @cxlm: cxl_mem instance to modify
> + * @cmds: bitmap of commands to mark available for userspace
> + */
> +void clear_exclusive_cxl_commands(struct cxl_mem *cxlm, unsigned long *cmds)
> +{
> +	down_write(&cxl_memdev_rwsem);
> +	bitmap_andnot(cxlm->exclusive_cmds, cxlm->exclusive_cmds, cmds,
> +		      CXL_MEM_COMMAND_ID_MAX);
> +	up_write(&cxl_memdev_rwsem);
> +}
> +EXPORT_SYMBOL_GPL(clear_exclusive_cxl_commands);
> +
>  static void cxl_memdev_shutdown(struct device *dev)
>  {
>  	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index 16201b7d82d2..468b7b8be207 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -101,6 +101,7 @@ struct cxl_mbox_cmd {
>   * @mbox_mutex: Mutex to synchronize mailbox access.
>   * @firmware_version: Firmware version for the memory device.
>   * @enabled_cmds: Hardware commands found enabled in CEL.
> + * @exclusive_cmds: Commands that are kernel-internal only
>   * @pmem_range: Active Persistent memory capacity configuration
>   * @ram_range: Active Volatile memory capacity configuration
>   * @total_bytes: sum of all possible capacities
> @@ -127,6 +128,7 @@ struct cxl_mem {
>  	struct mutex mbox_mutex; /* Protects device mailbox and firmware */
>  	char firmware_version[0x10];
>  	DECLARE_BITMAP(enabled_cmds, CXL_MEM_COMMAND_ID_MAX);
> +	DECLARE_BITMAP(exclusive_cmds, CXL_MEM_COMMAND_ID_MAX);
>  
>  	struct range pmem_range;
>  	struct range ram_range;
> @@ -200,4 +202,6 @@ int cxl_mem_identify(struct cxl_mem *cxlm);
>  int cxl_mem_enumerate_cmds(struct cxl_mem *cxlm);
>  int cxl_mem_create_range_info(struct cxl_mem *cxlm);
>  struct cxl_mem *cxl_mem_create(struct device *dev);
> +void set_exclusive_cxl_commands(struct cxl_mem *cxlm, unsigned long *cmds);
> +void clear_exclusive_cxl_commands(struct cxl_mem *cxlm, unsigned long *cmds);
>  #endif /* __CXL_MEM_H__ */
> diff --git a/drivers/cxl/pmem.c b/drivers/cxl/pmem.c
> index 9652c3ee41e7..a972af7a6e0b 100644
> --- a/drivers/cxl/pmem.c
> +++ b/drivers/cxl/pmem.c
> @@ -16,10 +16,7 @@
>   */
>  static struct workqueue_struct *cxl_pmem_wq;
>  
> -static void unregister_nvdimm(void *nvdimm)
> -{
> -	nvdimm_delete(nvdimm);
> -}
> +static __read_mostly DECLARE_BITMAP(exclusive_cmds, CXL_MEM_COMMAND_ID_MAX);
>  
>  static int match_nvdimm_bridge(struct device *dev, const void *data)
>  {
> @@ -36,12 +33,25 @@ static struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(void)
>  	return to_cxl_nvdimm_bridge(dev);
>  }
>  
> +static void cxl_nvdimm_remove(struct device *dev)
> +{
> +	struct cxl_nvdimm *cxl_nvd = to_cxl_nvdimm(dev);
> +	struct nvdimm *nvdimm = dev_get_drvdata(dev);
> +	struct cxl_memdev *cxlmd = cxl_nvd->cxlmd;
> +	struct cxl_mem *cxlm = cxlmd->cxlm;
> +
> +	nvdimm_delete(nvdimm);
> +	clear_exclusive_cxl_commands(cxlm, exclusive_cmds);
> +}
> +
>  static int cxl_nvdimm_probe(struct device *dev)
>  {
>  	struct cxl_nvdimm *cxl_nvd = to_cxl_nvdimm(dev);
> +	struct cxl_memdev *cxlmd = cxl_nvd->cxlmd;
> +	struct cxl_mem *cxlm = cxlmd->cxlm;
>  	struct cxl_nvdimm_bridge *cxl_nvb;
> +	struct nvdimm *nvdimm = NULL;
>  	unsigned long flags = 0;
> -	struct nvdimm *nvdimm;
>  	int rc = -ENXIO;
>  
>  	cxl_nvb = cxl_find_nvdimm_bridge();
> @@ -50,25 +60,32 @@ static int cxl_nvdimm_probe(struct device *dev)
>  
>  	device_lock(&cxl_nvb->dev);
>  	if (!cxl_nvb->nvdimm_bus)
> -		goto out;
> +		goto out_unlock;
> +
> +	set_exclusive_cxl_commands(cxlm, exclusive_cmds);
>  
>  	set_bit(NDD_LABELING, &flags);
> +	rc = -ENOMEM;
>  	nvdimm = nvdimm_create(cxl_nvb->nvdimm_bus, cxl_nvd, NULL, flags, 0, 0,
>  			       NULL);
> -	if (!nvdimm)
> -		goto out;
> +	dev_set_drvdata(dev, nvdimm);
>  
> -	rc = devm_add_action_or_reset(dev, unregister_nvdimm, nvdimm);
> -out:
> +out_unlock:
>  	device_unlock(&cxl_nvb->dev);
>  	put_device(&cxl_nvb->dev);
>  
> -	return rc;
> +	if (!nvdimm) {
> +		clear_exclusive_cxl_commands(cxlm, exclusive_cmds);
> +		return rc;
> +	}
> +
> +	return 0;
>  }
>  
>  static struct cxl_driver cxl_nvdimm_driver = {
>  	.name = "cxl_nvdimm",
>  	.probe = cxl_nvdimm_probe,
> +	.remove = cxl_nvdimm_remove,
>  	.id = CXL_DEVICE_NVDIMM,
>  };
>  
> @@ -194,6 +211,10 @@ static __init int cxl_pmem_init(void)
>  {
>  	int rc;
>  
> +	set_bit(CXL_MEM_COMMAND_ID_SET_PARTITION_INFO, exclusive_cmds);
> +	set_bit(CXL_MEM_COMMAND_ID_SET_SHUTDOWN_STATE, exclusive_cmds);
> +	set_bit(CXL_MEM_COMMAND_ID_SET_LSA, exclusive_cmds);
> +
>  	cxl_pmem_wq = alloc_ordered_workqueue("cxl_pmem", 0);
>  	if (!cxl_pmem_wq)
>  		return -ENXIO;
>