Re: [PATCH net-next v2 7/8] eth: mpnic: implement Rx queue allocation and cleanup

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- [Medium] In `mpnic_stop()`
  (drivers/net/ethernet/meta/mpnic/mpnic_netdev.c), Rx teardown frees…

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eth: mpnic: implement Rx queue allocation and cleanup

This commit adds the Rx side of the mpnic queue triad: a header buffer
queue, a payload buffer queue and a completion queue. All three share
one page pool per triad. It also adds the enable/disable, fill and
flush paths, and adds the HPQ, PPQ and RCQ blocks to the idle wait done
on teardown.

> diff --git a/drivers/net/ethernet/meta/mpnic/mpnic_txrx.c b/drivers/net/ethernet/meta/mpnic/mpnic_txrx.c
> index b1fb0d3902a7a..389a9e5476c6e 100644
> --- a/drivers/net/ethernet/meta/mpnic/mpnic_txrx.c
> +++ b/drivers/net/ethernet/meta/mpnic/mpnic_txrx.c

[ ... ]

> @@ -767,6 +1084,9 @@ void mpnic_wait_all_queues_idle(struct mpnic_dev *mpd)
>  		{ MPNIC_TQS_IDLE(0), MPNIC_TQS_IDLE_CNT, "TQS" },
>  		{ MPNIC_TDE_IDLE(0), MPNIC_TDE_IDLE_CNT, "TDE" },
>  		{ MPNIC_TCQ_IDLE(0), MPNIC_TCQ_IDLE_CNT, "TCQ" },
> +		{ MPNIC_HPQ_IDLE(0), MPNIC_HPQ_IDLE_CNT, "HPQ" },
> +		{ MPNIC_PPQ_IDLE(0), MPNIC_PPQ_IDLE_CNT, "PPQ" },
> +		{ MPNIC_RCQ_IDLE(0), MPNIC_RCQ_IDLE_CNT, "RCQ" },
>  	};
>  	u32 non_idle_bitmap;
>  	int err;
> @@ -779,15 +1099,31 @@ void mpnic_wait_all_queues_idle(struct mpnic_dev *mpd)
>  				non_idle_bitmap, err);
>  }
>  
> +static void mpnic_clean_bdq(struct mpnic_ring *bdq)
> +{
> +	unsigned int head = bdq->head;
> +
> +	while (head != bdq->tail) {
> +		struct page *page = bdq->rx_buf[head];
> +
> +		page_pool_put_full_page(page->pp, page, false);

[Severity: Medium]
What happens to these Rx buffers if the idle poll times out?
mpnic_wait_all_queues_idle() returns void. On timeout it only logs:

	err = read_poll_timeout(mpnic_non_idle_queues, non_idle_bitmap,
				!non_idle_bitmap, 20, 500000, false, mpd,
				queues, ARRAY_SIZE(queues));
	if (err)
		mpnic_idle_dump(mpd, queues, ARRAY_SIZE(queues),
				non_idle_bitmap, err);

mpnic_stop() then carries on with teardown either way:

	mpnic_disable(mpn);
	mpnic_wait_all_queues_idle(mpn->mpd);
	mpnic_flush(mpn);

	mpnic_reset_netif_queues(mpn);
	mpnic_free_resources(mpn);

Two things happen after that:

  - mpnic_flush()->mpnic_clean_bdq() gives every page still posted in
    [head, tail) back to the page pool.
  - mpnic_free_resources()->mpnic_free_rx_qt_resources() frees the HPQ,
    PPQ and RCQ descriptor rings with dma_free_coherent(), then calls
    page_pool_destroy().

Before this patch, the same timeout-and-continue path only covered Tx,
where the device reads host memory. Now there are DMA_FROM_DEVICE page
pool buffers and an RCQ that the device writes to.

If the device has not quiesced when the poll gives up, could it write
frame data into freed or reused pages, or write completions into the
freed RCQ ring?

Separately, the earlier commit "eth: mpnic: start and stop the Tx HW
queues" says every block a packet passes through must report idle
before memory is safe to free. The Rx idle table here covers HPQ, PPQ
and RCQ, but it has no Rx DMA engine entry to match TDE on the Tx side.
The only RDE registers defined are CFG, CTL and the MEM_INIT ones.

Does RCQ reporting idle guarantee that the RDE has no writes in flight?
If not, should an RDE idle entry be polled here as well?

This code is still the same at the end of the series, in "eth: mpnic:
add basic Rx handling".

> +
> +		head++;
> +		head &= bdq->size_mask;
> +	}
> +
> +	bdq->head = head;
> +}

[ ... ]

-- 
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