Subject: Re: [RFC PATCH v2 5/7] Revert "virtio_net: rx remove premapped failover code"

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 6 Sep 2024 06:12:35 -0400

On Fri, Sep 06, 2024 at 06:02:50PM +0800, Xuan Zhuo wrote:
> On Fri, 6 Sep 2024 05:52:36 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> > This reverts commit defd28aa5acb0fd7c15adc6bc40a8ac277d04dea.
> >
> > leads to crashes with no ACCESS_PLATFORM when
> > sysctl net.core.high_order_alloc_disable=1
> >
> > Cc: Xuan Zhuo <[email-masked]>
> > Reported-by: Si-Wei Liu <[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 0944430dfb1f..0a2ec9570521 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
> > @@ -867,7 +870,7 @@ 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;
> > @@ -880,6 +883,11 @@ 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;
> > @@ -905,42 +913,44 @@ 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);
> > @@ -957,9 +967,12 @@ 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;
> > +	}
> 
> This is too much code to revert. We can just revert this and next one.
> And add a patch to turn off the default premapped setting (return from this
> function directly). Otherwise, we will have to do all the work again in the
> future.
> 
> There is no need to revert xsk related code, xsk function cannot be enabled, in
> the case that premapped mode is not turned on. There is no direct impact itself.
> 
> Thanks.

I tried but quickly got lost as the automatic
revert did not work, and it's very close to release, so
I wanted to be sure it's right.

Post your own version of a revert for testing then please.

> 
> >  }
> >
> >  static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> > @@ -2107,7 +2120,8 @@ 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));
> >  	}
> >
> > @@ -2221,7 +2235,8 @@ 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));
> >  	}
> >
> > @@ -5392,7 +5407,7 @@ 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
> >