Re: [PATCH V3 2/3] md: propagate BLK_FEAT_PCI_P2PDMA from member devices to RAID device

On Fri, Apr 17, 2026 at 5:27 AM Chaitanya Kulkarni <[email protected]> wrote:
>
> From: Kiran Kumar Modukuri <[email protected]>
>
> MD RAID does not propagate BLK_FEAT_PCI_P2PDMA from member devices to
> the RAID device, preventing peer-to-peer DMA through the RAID layer even
> when all underlying devices support it.
>
> Enable BLK_FEAT_PCI_P2PDMA unconditionally in raid0, raid1 and raid10
> personalities during queue limits setup.  blk_stack_limits() clears it
> automatically if any member device lacks support, consistent with how
> BLK_FEAT_NOWAIT and BLK_FEAT_POLL are handled in the block core.
>
> Parity RAID personalities (raid4/5/6) are excluded because they require
> CPU access to data pages for parity computation, which is incompatible
> with P2P mappings.
>
> Tested with RAID0/1/10 arrays containing multiple NVMe devices with
> P2PDMA support, confirming that peer-to-peer transfers work correctly
> through the RAID layer.
>
> Signed-off-by: Kiran Kumar Modukuri <[email protected]>
> Signed-off-by: Chaitanya Kulkarni <[email protected]>
> ---
>  drivers/md/raid0.c  | 1 +
>  drivers/md/raid1.c  | 1 +
>  drivers/md/raid10.c | 1 +
>  3 files changed, 3 insertions(+)
>
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 5e38a51e349a..2cdaf7495d92 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -392,6 +392,7 @@ static int raid0_set_limits(struct mddev *mddev)
>         lim.io_opt = lim.io_min * mddev->raid_disks;
>         lim.chunk_sectors = mddev->chunk_sectors;
>         lim.features |= BLK_FEAT_ATOMIC_WRITES;
> +       lim.features |= BLK_FEAT_PCI_P2PDMA;
>         err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
>         if (err)
>                 return err;
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index ba91f7e61920..422ad4786569 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -3215,6 +3215,7 @@ static int raid1_set_limits(struct mddev *mddev)
>         lim.max_hw_wzeroes_unmap_sectors = 0;
>         lim.logical_block_size = mddev->logical_block_size;
>         lim.features |= BLK_FEAT_ATOMIC_WRITES;
> +       lim.features |= BLK_FEAT_PCI_P2PDMA;
>         err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
>         if (err)
>                 return err;
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 4901ebe45c87..07a5b734c8f3 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -3939,6 +3939,7 @@ static int raid10_set_queue_limits(struct mddev *mddev)
>         lim.chunk_sectors = mddev->chunk_sectors;
>         lim.io_opt = lim.io_min * raid10_nr_stripes(conf);
>         lim.features |= BLK_FEAT_ATOMIC_WRITES;
> +       lim.features |= BLK_FEAT_PCI_P2PDMA;
>         err = mddev_stack_rdev_limits(mddev, &lim, MDDEV_STACK_INTEGRITY);
>         if (err)
>                 return err;
> --
> 2.39.5
>
>

Thanks for enabling this feature. Looks good to me.
Reviewed-by: Xiao Ni <[email protected]>