Re: [PATCH v4 05/12] PCI: endpoint: pci-epf-vntb: Guard configfs writes after EPC attach

On Wed, May 13, 2026 at 11:49:16AM +0900, Koichiro Den wrote:
> db_count controls how many doorbell slots are allocated and exposed. It is
> also used by the doorbell mask helpers. After an EPC has been attached,
> changing it from configfs can leave runtime paths using a different count
> than the one used to set up the doorbell resources.
>
> Reject db_count writes after EPC attach, and reject values outside
> MIN_DB_COUNT..MAX_DB_COUNT before attach. Now that MIN_DB_COUNT documents
> the usable doorbell floor, use it in the store path too.
>
> While at it, apply the same after-attach guard to the other vNTB configfs
> knobs. BAR choices, spad_count, memory-window counts and sizes, and the
> virtual PCI IDs are also consumed during bind, so changing them later at
> runtime is meaningless and unsafe.
>
> Return -EOPNOTSUPP for after-attach writes. The value itself may be valid,
> but changing it in that state is not supported.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

> Changes since v3:
>   - New patch.
>
>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 41 ++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 818ae5999976..524355a8b4be 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -1020,6 +1020,11 @@ static void epf_ntb_epc_cleanup(struct epf_ntb *ntb)
>  	epf_ntb_config_sspad_bar_clear(ntb);
>  }
>
> +static bool epf_ntb_epc_attached(struct epf_ntb *ntb)
> +{
> +	return ntb->epf->epc || ntb->epf->sec_epc;
> +}
> +
>  #define EPF_NTB_R(_name)						\
>  static ssize_t epf_ntb_##_name##_show(struct config_item *item,		\
>  				      char *page)			\
> @@ -1039,6 +1044,9 @@ static ssize_t epf_ntb_##_name##_store(struct config_item *item,	\
>  	u32 val;							\
>  	int ret;							\
>  									\
> +	if (epf_ntb_epc_attached(ntb))					\
> +		return -EOPNOTSUPP;					\
> +									\
>  	ret = kstrtou32(page, 0, &val);					\
>  	if (ret)							\
>  		return ret;						\
> @@ -1081,6 +1089,9 @@ static ssize_t epf_ntb_##_name##_store(struct config_item *item,	\
>  	u64 val;							\
>  	int ret;							\
>  									\
> +	if (epf_ntb_epc_attached(ntb))					\
> +		return -EOPNOTSUPP;					\
> +									\
>  	ret = kstrtou64(page, 0, &val);					\
>  	if (ret)							\
>  		return ret;						\
> @@ -1119,6 +1130,9 @@ static ssize_t epf_ntb_##_name##_store(struct config_item *item,	\
>  		int val;						\
>  		int ret;						\
>  									\
> +		if (epf_ntb_epc_attached(ntb))				\
> +			return -EOPNOTSUPP;				\
> +									\
>  		ret = kstrtoint(page, 0, &val);				\
>  		if (ret)						\
>  			return ret;					\
> @@ -1139,6 +1153,9 @@ static ssize_t epf_ntb_num_mws_store(struct config_item *item,
>  	u32 val;
>  	int ret;
>
> +	if (epf_ntb_epc_attached(ntb))
> +		return -EOPNOTSUPP;
> +
>  	ret = kstrtou32(page, 0, &val);
>  	if (ret)
>  		return ret;
> @@ -1151,10 +1168,32 @@ static ssize_t epf_ntb_num_mws_store(struct config_item *item,
>  	return len;
>  }
>
> +static ssize_t epf_ntb_db_count_store(struct config_item *item,
> +				      const char *page, size_t len)
> +{
> +	struct config_group *group = to_config_group(item);
> +	struct epf_ntb *ntb = to_epf_ntb(group);
> +	u32 val;
> +	int ret;
> +
> +	if (epf_ntb_epc_attached(ntb))
> +		return -EOPNOTSUPP;
> +
> +	ret = kstrtou32(page, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val < MIN_DB_COUNT || val > MAX_DB_COUNT)
> +		return -EINVAL;
> +
> +	WRITE_ONCE(ntb->db_count, val);
> +
> +	return len;
> +}
> +
>  EPF_NTB_R(spad_count)
>  EPF_NTB_W(spad_count)
>  EPF_NTB_R(db_count)
> -EPF_NTB_W(db_count)
>  EPF_NTB_R(num_mws)
>  EPF_NTB_R(vbus_number)
>  EPF_NTB_W(vbus_number)
> --
> 2.51.0
>