netdev - Re: [PATCH bpf-next v4 07/11] mlx5e: modify driver for handling offsets

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Date:   Thu, 1 Aug 2019 10:05:26 +0000
From:   Maxim Mikityanskiy <maximmi@...lanox.com>
To:     Kevin Laatz <kevin.laatz@...el.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "bjorn.topel@...el.com" <bjorn.topel@...el.com>,
        "magnus.karlsson@...el.com" <magnus.karlsson@...el.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "bruce.richardson@...el.com" <bruce.richardson@...el.com>,
        "ciara.loftus@...el.com" <ciara.loftus@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [PATCH bpf-next v4 07/11] mlx5e: modify driver for handling
 offsets

On 2019-07-30 11:53, Kevin Laatz wrote:
> With the addition of the unaligned chunks option, we need to make sure we
> handle the offsets accordingly based on the mode we are currently running
> in. This patch modifies the driver to appropriately mask the address for
> each case.
> 
> Signed-off-by: Kevin Laatz <kevin.laatz@...el.com>

Please note that this patch doesn't actually add the support for the new 
feature, because the validation checks in mlx5e_rx_get_linear_frag_sz 
and mlx5e_validate_xsk_param need to be relaxed. Currently the frame 
size of PAGE_SIZE is forced, and the fragment size is increased to 
PAGE_SIZE in case of XDP (including XSK).

After making the changes required to permit frame sizes smaller than 
PAGE_SIZE, our Striding RQ feature will be used in a way we haven't used 
it before, so we need to verify with the hardware team that this usage 
is legitimate.

> ---
> v3:
>    - Use new helper function to handle offset
> 
> v4:
>    - fixed headroom addition to handle. Using xsk_umem_adjust_headroom()
>      now.
> ---
>   drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c    | 8 ++++++--
>   drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c | 3 ++-
>   2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> index b0b982cf69bb..d5245893d2c8 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> @@ -122,6 +122,7 @@ bool mlx5e_xdp_handle(struct mlx5e_rq *rq, struct mlx5e_dma_info *di,
>   		      void *va, u16 *rx_headroom, u32 *len, bool xsk)
>   {
>   	struct bpf_prog *prog = READ_ONCE(rq->xdp_prog);
> +	struct xdp_umem *umem = rq->umem;
>   	struct xdp_buff xdp;
>   	u32 act;
>   	int err;
> @@ -138,8 +139,11 @@ bool mlx5e_xdp_handle(struct mlx5e_rq *rq, struct mlx5e_dma_info *di,
>   	xdp.rxq = &rq->xdp_rxq;
>   
>   	act = bpf_prog_run_xdp(prog, &xdp);
> -	if (xsk)
> -		xdp.handle += xdp.data - xdp.data_hard_start;
> +	if (xsk) {
> +		u64 off = xdp.data - xdp.data_hard_start;
> +
> +		xdp.handle = xsk_umem_handle_offset(umem, xdp.handle, off);
> +	}
>   	switch (act) {
>   	case XDP_PASS:
>   		*rx_headroom = xdp.data - xdp.data_hard_start;
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
> index 6a55573ec8f2..7c49a66d28c9 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
> @@ -24,7 +24,8 @@ int mlx5e_xsk_page_alloc_umem(struct mlx5e_rq *rq,
>   	if (!xsk_umem_peek_addr_rq(umem, &handle))
>   		return -ENOMEM;
>   
> -	dma_info->xsk.handle = handle + rq->buff.umem_headroom;
> +	dma_info->xsk.handle = xsk_umem_adjust_offset(umem, handle,
> +						      rq->buff.umem_headroom);
>   	dma_info->xsk.data = xdp_umem_get_data(umem, dma_info->xsk.handle);
>   
>   	/* No need to add headroom to the DMA address. In striding RQ case, we
>