Subject: Re: [PATCH RFC 1/3] Revert "virtio_net: rx remove premapped failover code"

From: Darren Kenny <[email-masked]>
Date: Wed, 14 Aug 2024 16:19:06 +0100

Hi Michael,

I've tested this on the system that was reproducing the panic, and it
everything is working now as expected.

For the series then:

Tested-by: Darren Kenny <[email-masked]>

Thanks,

Darren.

On Wednesday, 2024-08-14 at 02:59:20 -04, Michael S. Tsirkin wrote:
> This reverts commit defd28aa5acb0fd7c15adc6bc40a8ac277d04dea.
>
> leads to crashes with no ACCESS_PLATFORM when
> sysctl net.core.high_order_alloc_disable=1
>
> Reported-by: Si-Wei Liu <[email-masked]>
> Message-ID: <[email-masked]>
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 89 +++++++++++++++++++++++-----------------
>  1 file changed, 52 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fd3d7e926022..4f7e686b8bf9 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -348,6 +348,9 @@ struct receive_queue {
>  
>  	/* Record the last dma info to free after new pages is allocated. */
>  	struct virtnet_rq_dma *last_dma;
> +
> +	/* Do dma by self */
> +	bool do_dma;
>  };
>  
>  /* This structure can contain rss message with maximum settings for indirection table and keysize
> @@ -848,7 +851,7 @@ static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
>  	void *buf;
>  
>  	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> -	if (buf)
> +	if (buf && rq->do_dma)
>  		virtnet_rq_unmap(rq, buf, *len);
>  
>  	return buf;
> @@ -861,6 +864,11 @@ static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
>  	u32 offset;
>  	void *head;
>  
> +	if (!rq->do_dma) {
> +		sg_init_one(rq->sg, buf, len);
> +		return;
> +	}
> +
>  	head = page_address(rq->alloc_frag.page);
>  
>  	offset = buf - head;
> @@ -886,42 +894,44 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>  
>  	head = page_address(alloc_frag->page);
>  
> -	dma = head;
> +	if (rq->do_dma) {
> +		dma = head;
>  
> -	/* new pages */
> -	if (!alloc_frag->offset) {
> -		if (rq->last_dma) {
> -			/* Now, the new page is allocated, the last dma
> -			 * will not be used. So the dma can be unmapped
> -			 * if the ref is 0.
> +		/* new pages */
> +		if (!alloc_frag->offset) {
> +			if (rq->last_dma) {
> +				/* Now, the new page is allocated, the last dma
> +				 * will not be used. So the dma can be unmapped
> +				 * if the ref is 0.
> +				 */
> +				virtnet_rq_unmap(rq, rq->last_dma, 0);
> +				rq->last_dma = NULL;
> +			}
> +
> +			dma->len = alloc_frag->size - sizeof(*dma);
> +
> +			addr = virtqueue_dma_map_single_attrs(rq->vq, dma + 1,
> +							      dma->len, DMA_FROM_DEVICE, 0);
> +			if (virtqueue_dma_mapping_error(rq->vq, addr))
> +				return NULL;
> +
> +			dma->addr = addr;
> +			dma->need_sync = virtqueue_dma_need_sync(rq->vq, addr);
> +
> +			/* Add a reference to dma to prevent the entire dma from
> +			 * being released during error handling. This reference
> +			 * will be freed after the pages are no longer used.
>  			 */
> -			virtnet_rq_unmap(rq, rq->last_dma, 0);
> -			rq->last_dma = NULL;
> +			get_page(alloc_frag->page);
> +			dma->ref = 1;
> +			alloc_frag->offset = sizeof(*dma);
> +
> +			rq->last_dma = dma;
>  		}
>  
> -		dma->len = alloc_frag->size - sizeof(*dma);
> -
> -		addr = virtqueue_dma_map_single_attrs(rq->vq, dma + 1,
> -						      dma->len, DMA_FROM_DEVICE, 0);
> -		if (virtqueue_dma_mapping_error(rq->vq, addr))
> -			return NULL;
> -
> -		dma->addr = addr;
> -		dma->need_sync = virtqueue_dma_need_sync(rq->vq, addr);
> -
> -		/* Add a reference to dma to prevent the entire dma from
> -		 * being released during error handling. This reference
> -		 * will be freed after the pages are no longer used.
> -		 */
> -		get_page(alloc_frag->page);
> -		dma->ref = 1;
> -		alloc_frag->offset = sizeof(*dma);
> -
> -		rq->last_dma = dma;
> +		++dma->ref;
>  	}
>  
> -	++dma->ref;
> -
>  	buf = head + alloc_frag->offset;
>  
>  	get_page(alloc_frag->page);
> @@ -938,9 +948,12 @@ static void virtnet_rq_set_premapped(struct virtnet_info *vi)
>  	if (!vi->mergeable_rx_bufs && vi->big_packets)
>  		return;
>  
> -	for (i = 0; i < vi->max_queue_pairs; i++)
> -		/* error should never happen */
> -		BUG_ON(virtqueue_set_dma_premapped(vi->rq[i].vq));
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		if (virtqueue_set_dma_premapped(vi->rq[i].vq))
> +			continue;
> +
> +		vi->rq[i].do_dma = true;
> +	}
>  }
>  
>  static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> @@ -2036,7 +2049,8 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>  
>  	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
>  	if (err < 0) {
> -		virtnet_rq_unmap(rq, buf, 0);
> +		if (rq->do_dma)
> +			virtnet_rq_unmap(rq, buf, 0);
>  		put_page(virt_to_head_page(buf));
>  	}
>  
> @@ -2150,7 +2164,8 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>  	ctx = mergeable_len_to_ctx(len + room, headroom);
>  	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
>  	if (err < 0) {
> -		virtnet_rq_unmap(rq, buf, 0);
> +		if (rq->do_dma)
> +			virtnet_rq_unmap(rq, buf, 0);
>  		put_page(virt_to_head_page(buf));
>  	}
>  
> @@ -5231,7 +5246,7 @@ static void free_receive_page_frags(struct virtnet_info *vi)
>  	int i;
>  	for (i = 0; i < vi->max_queue_pairs; i++)
>  		if (vi->rq[i].alloc_frag.page) {
> -			if (vi->rq[i].last_dma)
> +			if (vi->rq[i].do_dma && vi->rq[i].last_dma)
>  				virtnet_rq_unmap(&vi->rq[i], vi->rq[i].last_dma, 0);
>  			put_page(vi->rq[i].alloc_frag.page);
>  		}
> -- 
> MST