Re: [PATCH] cxl/pmem: Format nvdimm serial numbers as decimal

[Dave Jiang <dave.jiang@intel.com>]

On 6/18/26 10:59 PM, Alison Schofield wrote:
> The CXL NVDIMM security passphrase key is looked up by the description
> "nvdimm:" followed by the device serial string. For serial numbers of
> 10 and above, the kernel auto-unlock path fails to find the key
> because ndctl names it with a decimal serial and the kernel uses hex.
> 
> That means a passphrase-protected device cannot be unlocked after a
> reboot, and the pmem namespaces it backs do not come up. Devices
> without an enrolled passphrase are unaffected.
> 
> The mismatch occurs for any serial number of 10 and above. Since CXL
> device serial numbers are vendor-assigned 64-bit values, that covers
> essentially all real hardware once security is enabled.
> 
> The 'id' sysfs attribute is established ABI that ndctl consumes as
> decimal, so format the kernel's serial string the same way. A u64
> decimal string requires up to 20 digits plus a NUL byte, so grow
> CXL_DEV_ID_LEN to fit it.
> 
> The issue was exposed by CXL unit test cxl-security.sh when cxl_test
> mock serial numbers were recently extended to 10 and above.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: b5807c80b5bc ("cxl: add dimm_id support for __nvdimm_create()")
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> ---
>  drivers/cxl/core/pmem.c | 10 ++++++----
>  drivers/cxl/cxl.h       |  3 ++-
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cxl/core/pmem.c b/drivers/cxl/core/pmem.c
> index 68462e38a977..2ccdf04c1f43 100644
> --- a/drivers/cxl/core/pmem.c
> +++ b/drivers/cxl/core/pmem.c
> @@ -219,12 +219,14 @@ static struct cxl_nvdimm *cxl_nvdimm_alloc(struct cxl_nvdimm_bridge *cxl_nvb,
>  	dev->bus = &cxl_bus_type;
>  	dev->type = &cxl_nvdimm_type;
>  	/*
> -	 * A "%llx" string is 17-bytes vs dimm_id that is max
> -	 * NVDIMM_KEY_DESC_LEN
> +	 * dev_id becomes the nvdimm dimm_id used for security key
> +	 * lookups. Match the decimal serial emitted by the CXL 'id'
> +	 * sysfs attribute. A u64 decimal string requires 20 digits
> +	 * plus a NUL byte and must still fit in NVDIMM_KEY_DESC_LEN.
>  	 */
> -	BUILD_BUG_ON(sizeof(cxl_nvd->dev_id) < 17 ||
> +	BUILD_BUG_ON(sizeof(cxl_nvd->dev_id) < 21 ||

Can CXL_DEV_ID_LEN be used here?

>  		     sizeof(cxl_nvd->dev_id) > NVDIMM_KEY_DESC_LEN);
> -	sprintf(cxl_nvd->dev_id, "%llx", cxlmd->cxlds->serial);
> +	sprintf(cxl_nvd->dev_id, "%lld", cxlmd->cxlds->serial);
>  
>  	return cxl_nvd;
>  }
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 1297594beaec..3463faeb8a15 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -487,7 +487,8 @@ struct cxl_nvdimm_bridge {
>  	struct nvdimm_bus_descriptor nd_desc;
>  };
>  
> -#define CXL_DEV_ID_LEN 19
> +/* Holds a u64 serial as a decimal string: up to 20 digits + NUL */
> +#define CXL_DEV_ID_LEN 21
>  
>  enum {
>  	CXL_NVD_F_INVALIDATED = 0,
> 
> base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6