Re: [PATCH 1/2] PCI: endpoint: pci-epf-vntb: Add check to detect 'db_count' value of 0

On Tue, Apr 07, 2026 at 06:14:20PM +0530, Manivannan Sadhasivam wrote:
> From: Manivannan Sadhasivam <[email protected]>
> 
> epf_ntb::db_count value should be within 1 to MAX_DB_COUNT. Current code
> only checks for the upper bound, while the lower bound is unchecked. This
> can cause a lot of issues in the driver if the user passes 'db_count' as 0.
> 
> So add a check for 0 also. While at it, remove the redundant 'db_count'
> assignment.
> 
> Fixes: e35f56bb0330 ("PCI: endpoint: Support NTB transfer between RC and EP")
> Signed-off-by: Manivannan Sadhasivam <[email protected]>
> ---

I noticed this one is still floating around. In case one more R-b helps:

Reviewed-by: Koichiro Den <[email protected]>

P.S. For pci-epf-vntb, I think ntb->db_count needs to be at least 3 in practice
for doorbells to be useful, because of the link event slot (#0) and a
historically skipped slot (#1). Still, as a standalone fix, this patch looks
good to me.

>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 2256c3062b1a..3d30aa4dbb84 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -483,7 +483,6 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
>  {
>  	const struct pci_epc_features *epc_features;
>  	struct device *dev;
> -	u32 db_count;
>  	int ret;
>  
>  	dev = &ntb->epf->dev;
> @@ -495,14 +494,12 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
>  		return -EINVAL;
>  	}
>  
> -	db_count = ntb->db_count;
> -	if (db_count > MAX_DB_COUNT) {
> -		dev_err(dev, "DB count cannot be more than %d\n", MAX_DB_COUNT);
> +	if (!ntb->db_count || ntb->db_count > MAX_DB_COUNT) {
> +		dev_err(dev, "DB count %d out of range (1 - %d)\n",
> +			ntb->db_count, MAX_DB_COUNT);
>  		return -EINVAL;
>  	}
>  
> -	ntb->db_count = db_count;
> -
>  	if (epc_features->msi_capable) {
>  		ret = pci_epc_set_msi(ntb->epf->epc,
>  				      ntb->epf->func_no,
> -- 
> 2.51.0
>