Subject: Re: [PATCH v2 24/27] nvdimm/ocxl: Implement Overwrite

From: Jonathan Cameron <[email-masked]>
Date: Mon, 3 Feb 2020 15:10:19 +0000

On Tue, 3 Dec 2019 14:46:52 +1100
Alastair D'Silva <[email-masked]> wrote:

> From: Alastair D'Silva <[email-masked]>
> 
> The near storage command 'Secure Erase' overwrites all data on the
> media.
> 
> This patch hooks it up to the security function 'overwrite'.
> 
> Signed-off-by: Alastair D'Silva <[email-masked]>

A few things to tidy up in here.

Thanks,

Jonathan

> ---
>  drivers/nvdimm/ocxl/scm.c          | 164 ++++++++++++++++++++++++++++-
>  drivers/nvdimm/ocxl/scm_internal.c |   1 +
>  drivers/nvdimm/ocxl/scm_internal.h |  17 +++
>  3 files changed, 180 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvdimm/ocxl/scm.c b/drivers/nvdimm/ocxl/scm.c
> index a81eb5916eb3..8deb7862793c 100644
> --- a/drivers/nvdimm/ocxl/scm.c
> +++ b/drivers/nvdimm/ocxl/scm.c
> @@ -169,6 +169,86 @@ static int scm_reserve_metadata(struct scm_data *scm_data,
>  	return 0;
>  }
>  
> +/**
> + * scm_overwrite() - Overwrite all data on the card
> + * @scm_data: The SCM device data

I would mention in here that this exists with the lock held and
where that is unlocked again.

> + * Return: 0 on success
> + */
> +int scm_overwrite(struct scm_data *scm_data)
> +{
> +	int rc;
> +
> +	mutex_lock(&scm_data->ns_command.lock);
> +
> +	rc = scm_ns_command_request(scm_data, NS_COMMAND_SECURE_ERASE);
> +	if (rc)

Perhaps change that goto label to reflect it is the error path rather
than a shared exit route.

> +		goto out;
> +
> +	rc = scm_ns_command_execute(scm_data);
> +	if (rc)
> +		goto out;
> +
> +	scm_data->overwrite_state = SCM_OVERWRITE_BUSY;
> +
> +	return 0;
> +
> +out:
> +	mutex_unlock(&scm_data->ns_command.lock);
> +	return rc;
> +}
> +
> +/**
> + * scm_secop_overwrite() - Overwrite all data on the card
> + * @nvdimm: The nvdimm representation of the SCM device to start the overwrite on
> + * @key_data: Unused (no security key implementation)
> + * Return: 0 on success
> + */
> +static int scm_secop_overwrite(struct nvdimm *nvdimm,
> +			       const struct nvdimm_key_data *key_data)
> +{
> +	struct scm_data *scm_data = nvdimm_provider_data(nvdimm);
> +
> +	return scm_overwrite(scm_data);
> +}
> +
> +/**
> + * scm_secop_query_overwrite() - Get the current overwrite state
> + * @nvdimm: The nvdimm representation of the SCM device to start the overwrite on
> + * Return: 0 if successful or idle, -EBUSY if busy, -EFAULT if failed
> + */
> +static int scm_secop_query_overwrite(struct nvdimm *nvdimm)
> +{
> +	struct scm_data *scm_data = nvdimm_provider_data(nvdimm);
> +
> +	if (scm_data->overwrite_state == SCM_OVERWRITE_BUSY)
> +		return -EBUSY;
> +
> +	if (scm_data->overwrite_state == SCM_OVERWRITE_FAILED)
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +/**
> + * scm_secop_get_flags() - return the security flags for the SCM device

All params need to documented in kernel-doc comments.

> + */
> +static unsigned long scm_secop_get_flags(struct nvdimm *nvdimm,
> +		enum nvdimm_passphrase_type ptype)
> +{
> +	struct scm_data *scm_data = nvdimm_provider_data(nvdimm);
> +
> +	if (scm_data->overwrite_state == SCM_OVERWRITE_BUSY)
> +		return BIT(NVDIMM_SECURITY_OVERWRITE);
> +
> +	return BIT(NVDIMM_SECURITY_DISABLED);
> +}
> +
> +static const struct nvdimm_security_ops sec_ops  = {
> +	.get_flags = scm_secop_get_flags,
> +	.overwrite = scm_secop_overwrite,
> +	.query_overwrite = scm_secop_query_overwrite,
> +};
> +
>  /**
>   * scm_register_lpc_mem() - Discover persistent memory on a device and register it with the NVDIMM subsystem
>   * @scm_data: The SCM device data
> @@ -224,10 +304,10 @@ static int scm_register_lpc_mem(struct scm_data *scm_data)
>  	set_bit(NDD_ALIASING, &nvdimm_flags);
>  
>  	snprintf(serial, sizeof(serial), "%llx", fn_config->serial);
> -	nd_mapping_desc.nvdimm = nvdimm_create(scm_data->nvdimm_bus, scm_data,
> +	nd_mapping_desc.nvdimm = __nvdimm_create(scm_data->nvdimm_bus, scm_data,
>  				 scm_dimm_attribute_groups,
>  				 nvdimm_flags, nvdimm_cmd_mask,
> -				 0, NULL);
> +				 0, NULL, serial, &sec_ops);
>  	if (!nd_mapping_desc.nvdimm)
>  		return -ENOMEM;
>  
> @@ -1530,6 +1610,83 @@ static void scm_dump_error_log(struct scm_data *scm_data)
>  	kfree(buf);
>  }
>  
> +static void scm_handle_nscra_doorbell(struct scm_data *scm_data)
> +{
> +	int rc;
> +
> +	if (scm_data->ns_command.op_code == NS_COMMAND_SECURE_ERASE) {

Feels likely that we are going to end up with quite a few blocks like this as
the driver is extended. Perhaps just start out with a switch statement and
separate functions that it calls?

> +		u64 success, attempted;
> +

One is enough here.

> +
> +		rc = scm_ns_response(scm_data);
> +		if (rc < 0) {
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;

If this were a separate function as suggested above, I'd use a goto to ensure we
unlock in all paths.

> +			mutex_unlock(&scm_data->ns_command.lock);
> +			return;
> +		}
> +		if (rc != STATUS_SUCCESS)
> +			scm_warn_status(scm_data, "Unexpected status from overwrite", rc);
> +
> +		rc = ocxl_global_mmio_read64(scm_data->ocxl_afu,
> +					     scm_data->ns_command.response_offset +
> +					     NS_RESPONSE_SECURE_ERASE_ACCESSIBLE_SUCCESS,
> +					     OCXL_HOST_ENDIAN, &success);
> +		if (rc) {
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;
> +			mutex_unlock(&scm_data->ns_command.lock);
> +			return;
> +		}
> +
> +		rc = ocxl_global_mmio_read64(scm_data->ocxl_afu,
> +					     scm_data->ns_command.response_offset +
> +					     NS_RESPONSE_SECURE_ERASE_ACCESSIBLE_ATTEMPTED,
> +					     OCXL_HOST_ENDIAN, &attempted);
> +		if (rc) {
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;
> +			mutex_unlock(&scm_data->ns_command.lock);
> +			return;
> +		}
> +
> +		scm_data->overwrite_state = SCM_OVERWRITE_SUCCESS;
> +		if (success != attempted)
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;
> +
> +		dev_info(&scm_data->dev,
> +			 "Overwritten %llu/%llu accessible pages", success, attempted);

Do we want to spam the log?  Feels like dev_dbg maybe?

> +
> +		rc = ocxl_global_mmio_read64(scm_data->ocxl_afu,
> +					     scm_data->ns_command.response_offset +
> +					     NS_RESPONSE_SECURE_ERASE_DEFECTIVE_SUCCESS,
> +					     OCXL_HOST_ENDIAN, &success);
> +		if (rc) {
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;
> +			mutex_unlock(&scm_data->ns_command.lock);
> +			return;
> +		}
> +
> +		rc = ocxl_global_mmio_read64(scm_data->ocxl_afu,
> +					     scm_data->ns_command.response_offset +
> +					     NS_RESPONSE_SECURE_ERASE_DEFECTIVE_ATTEMPTED,
> +					     OCXL_HOST_ENDIAN, &attempted);
> +		if (rc) {
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;
> +			mutex_unlock(&scm_data->ns_command.lock);
> +			return;
> +		}
> +
> +		if (success != attempted)
> +			scm_data->overwrite_state = SCM_OVERWRITE_FAILED;
> +
> +		dev_info(&scm_data->dev,
> +			 "Overwritten %llu/%llu defective pages", success, attempted);

Again, maybe dev_dbg?

> +
> +		scm_ns_response_handled(scm_data);
> +
> +		mutex_unlock(&scm_data->ns_command.lock);
> +		return;
> +	}
> +}
> +
>  static irqreturn_t scm_imn0_handler(void *private)
>  {
>  	struct scm_data *scm_data = private;
> @@ -1537,6 +1694,9 @@ static irqreturn_t scm_imn0_handler(void *private)
>  
>  	(void)scm_chi(scm_data, &chi);
>  
> +	if (chi & GLOBAL_MMIO_CHI_NSCRA)
> +		scm_handle_nscra_doorbell(scm_data);
> +
>  	if (chi & GLOBAL_MMIO_CHI_ELA) {
>  		dev_warn(&scm_data->dev, "Error log is available\n");
>  
> diff --git a/drivers/nvdimm/ocxl/scm_internal.c b/drivers/nvdimm/ocxl/scm_internal.c
> index 8fc849610eaa..db919a23c69b 100644
> --- a/drivers/nvdimm/ocxl/scm_internal.c
> +++ b/drivers/nvdimm/ocxl/scm_internal.c
> @@ -173,6 +173,7 @@ int scm_ns_response_handled(const struct scm_data *scm_data)
>  				      OCXL_LITTLE_ENDIAN, GLOBAL_MMIO_CHI_NSCRA);
>  }
>  
> +

Stray blank line..

>  void scm_warn_status(const struct scm_data *scm_data, const char *message,
>  		     u8 status)
>  {
> diff --git a/drivers/nvdimm/ocxl/scm_internal.h b/drivers/nvdimm/ocxl/scm_internal.h
> index af19813a7f75..4a29088612a9 100644
> --- a/drivers/nvdimm/ocxl/scm_internal.h
> +++ b/drivers/nvdimm/ocxl/scm_internal.h
> @@ -70,6 +70,15 @@
>  #define ADMIN_COMMAND_CMD_CAPS		0x08u
>  #define ADMIN_COMMAND_MAX		0x08u
>  
> +#define NS_COMMAND_SECURE_ERASE	0x20ull
> +
> +#define NS_RESPONSE_SECURE_ERASE_ACCESSIBLE_SUCCESS 0x20
> +#define NS_RESPONSE_SECURE_ERASE_ACCESSIBLE_ATTEMPTED 0x28
> +#define NS_RESPONSE_SECURE_ERASE_DEFECTIVE_SUCCESS 0x30
> +#define NS_RESPONSE_SECURE_ERASE_DEFECTIVE_ATTEMPTED 0x38
> +

Lot of blank lines...

> +
> +
>  #define STATUS_SUCCESS		0x00
>  #define STATUS_MEM_UNAVAILABLE	0x20
>  #define STATUS_BAD_OPCODE	0x50
> @@ -99,6 +108,13 @@ struct scm_function_0 {
>  	struct ocxl_fn *ocxl_fn;
>  };
>  
> +enum overwrite_state {
> +	SCM_OVERWRITE_IDLE = 0,
> +	SCM_OVERWRITE_BUSY,
> +	SCM_OVERWRITE_SUCCESS,
> +	SCM_OVERWRITE_FAILED
> +};
> +
>  struct scm_data {
>  	struct device dev;
>  	struct pci_dev *pdev;
> @@ -116,6 +132,7 @@ struct scm_data {
>  	void *metadata_addr;
>  	struct command_metadata admin_command;
>  	struct command_metadata ns_command;
> +	enum overwrite_state overwrite_state;
>  	struct resource scm_res;
>  	struct nd_region *nd_region;
>  	struct eventfd_ctx *ev_ctx;