Re: [PATCH v7 10/10] NTB: ntb_hw_epf: Support DMA and MW sharing a BAR

[Frank Li]

On Wed, Oct 21, 2026 at 01:22:29PM +0900, Koichiro Den wrote:
> A vNTB endpoint can place DMA resources after an MW in the same BAR.
> Limit the MW to the advertised boundary so clients cannot overwrite
> those resources.
>
> Advertise this support in LINK_UP, including when DMA is unavailable.
> Older endpoints ignore the argument.

if ignore it, any side effect? Does host DMA side use wrong memory region,
which actually is not mapped by EP?

Frank

>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---
> Changes since v6:
>   - Split from the BAR-sharing patch. (Frank)
>   - Advertise MW/DMA BAR boundary support in LINK_UP.
>
>  drivers/ntb/hw/epf/ntb_hw_epf.c | 46 +++++++++++++++++++++++++++------
>  1 file changed, 38 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> index e0016128b95c..56185870cba9 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -382,6 +382,23 @@ static int ntb_epf_mw_to_bar(struct ntb_epf_dev *ndev, int idx)
>  	return ndev->barno_map[BAR_MW1 + idx];
>  }
>
> +static resource_size_t ntb_epf_mw_offset(struct ntb_epf_dev *ndev, int idx)
> +{
> +	return !idx ? readl(ndev->ctrl_reg + NTB_EPF_CTRL(mw1_offset)) : 0;
> +}
> +
> +static resource_size_t ntb_epf_mw_size(struct ntb_epf_dev *ndev, int bar)
> +{
> +	resource_size_t end;
> +
> +	end = pci_resource_len(ndev->ntb.pdev, bar);
> +	/* The DMA submap offset marks the end of an MW sharing this BAR. */
> +	if (ndev->dma.submap.size && ndev->dma.submap.bar == bar)
> +		end = min(end, ndev->dma.submap.offset);
> +
> +	return end;
> +}
> +
>  static int ntb_epf_mw_count(struct ntb_dev *ntb, int pidx)
>  {
>  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
> @@ -420,7 +437,7 @@ static int ntb_epf_mw_get_align(struct ntb_dev *ntb, int pidx, int idx,
>  		*size_align = 1;
>
>  	if (size_max)
> -		*size_max = pci_resource_len(ndev->ntb.pdev, bar);
> +		*size_max = ntb_epf_mw_size(ndev, bar);
>
>  	return 0;
>  }
> @@ -524,7 +541,8 @@ static int ntb_epf_link_enable(struct ntb_dev *ntb,
>  	struct device *dev = ndev->dev;
>  	int ret;
>
> -	ret = ntb_epf_send_command(ndev, EPF_NTB_COMMAND_LINK_UP, 0);
> +	ret = ntb_epf_send_command(ndev, EPF_NTB_COMMAND_LINK_UP,
> +				   EPF_NTB_LINK_UP_DMA_MW_SUPPORTED);
>  	if (ret) {
>  		dev_err(dev, "Fail to enable link\n");
>  		return ret;
> @@ -707,7 +725,7 @@ static int ntb_epf_mw_set_trans(struct ntb_dev *ntb, int pidx, int idx,
>  	if (bar < 0)
>  		return bar;
>
> -	mw_size = pci_resource_len(ntb->pdev, bar);
> +	mw_size = ntb_epf_mw_size(ndev, bar);
>
>  	if (size > mw_size) {
>  		dev_err(dev, "Size:%pa is greater than the MW size %pa\n",
> @@ -739,21 +757,20 @@ static int ntb_epf_peer_mw_get_addr(struct ntb_dev *ntb, int idx,
>  				    phys_addr_t *base, resource_size_t *size)
>  {
>  	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
> -	u32 offset = 0;
> +	resource_size_t offset;
>  	int bar;
>
> -	if (idx == 0)
> -		offset = readl(ndev->ctrl_reg + NTB_EPF_CTRL(mw1_offset));
> -
>  	bar = ntb_epf_mw_to_bar(ndev, idx);
>  	if (bar < 0)
>  		return bar;
>
> +	offset = ntb_epf_mw_offset(ndev, idx);
> +
>  	if (base)
>  		*base = pci_resource_start(ndev->ntb.pdev, bar) + offset;
>
>  	if (size)
> -		*size = pci_resource_len(ndev->ntb.pdev, bar) - offset;
> +		*size = ntb_epf_mw_size(ndev, bar) - offset;
>
>  	return 0;
>  }
> @@ -851,6 +868,7 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
>  {
>  	struct device *dev = ndev->dev;
>  	int ret;
> +	int i;
>
>  	ndev->mw_count = readl(ndev->ctrl_reg + NTB_EPF_CTRL(num_mws));
>  	if (ndev->mw_count > NTB_EPF_MAX_MW_COUNT) {
> @@ -862,6 +880,18 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
>  		dev_err(dev, "Invalid endpoint DMA layout\n");
>  		return ret;
>  	}
> +	if (ndev->dma.submap.size) {
> +		for (i = 0; i < ndev->mw_count; i++) {
> +			int bar = ntb_epf_mw_to_bar(ndev, i);
> +
> +			if (bar == ndev->dma.submap.bar &&
> +			    ntb_epf_mw_size(ndev, bar) <=
> +			    ntb_epf_mw_offset(ndev, i)) {
> +				dev_err(dev, "Invalid DMA/MW boundary\n");
> +				return -EINVAL;
> +			}
> +		}
> +	}
>
>  	/* One Link interrupt and rest doorbell interrupt */
>  	ret = ntb_epf_init_isr(ndev, NTB_EPF_MIN_DB_COUNT + 1,
> --
> 2.54.0
>