Re: [PATCH net-next 04/13] virtio_ring: perform premapped operations based on per-buffer
From: Jason Wang <hidden>
Date: 2024-09-11 03:54:41
Also in:
bpf, virtualization
On Tue, Aug 20, 2024 at 3:33 PM Xuan Zhuo [off-list ref] wrote:
The current configuration sets the virtqueue (vq) to premapped mode, implying that all buffers submitted to this queue must be mapped ahead of time. This presents a challenge for the virtnet send queue (sq): the virtnet driver would be required to keep track of dma information for vq size * 17, which can be substantial. However, if the premapped mode were applied on a per-buffer basis, the complexity would be greatly reduced. With AF_XDP enabled, AF_XDP buffers would become premapped, while kernel skb buffers could remain unmapped.
Is this only applied to TX or both TX and RX.
We can distinguish them by sg_page(sg), When sg_page(sg) is NULL, this indicates that the driver has performed DMA mapping in advance, allowing the Virtio core to directly utilize sg_dma_address(sg) without conducting any internal DMA mapping.
This seems conflict with the code below? #define sg_is_premapped(sg) (!sg_page(sg)) And rethink of the design, a question is that is there a chance that VM_PFNMAP area could be used for virtio-net? If it is true, the trick for sg_page() can not work? A quick glance told me AF_XEP seems to be safe as it uses pin_user_pages(), but we need to check other possibilities. Or we need to fall back to our previous idea, having new APIs.
quoted hunk ↗ jump to hunk
Additionally, DMA unmap operations for this buffer will be bypassed. Suggested-by: Jason Wang <redacted> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> --- drivers/virtio/virtio_ring.c | 70 +++++++++++++++++++++--------------- 1 file changed, 41 insertions(+), 29 deletions(-)diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index b43eca93015c..7efddc71af67 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c@@ -235,6 +235,7 @@ static void vring_free(struct virtqueue *_vq); */ #define to_vvq(_vq) container_of_const(_vq, struct vring_virtqueue, vq) +#define sg_is_premapped(sg) (!sg_page(sg)) static bool virtqueue_use_indirect(const struct vring_virtqueue *vq, unsigned int total_sg)@@ -292,9 +293,10 @@ static bool vring_use_dma_api(const struct virtio_device *vdev) return false; } -static bool vring_need_unmap_buffer(const struct vring_virtqueue *vring) +static bool vring_need_unmap_buffer(const struct vring_virtqueue *vring, + const struct vring_desc_extra *extra) { - return vring->use_dma_api && !vring->premapped; + return vring->use_dma_api && (extra->addr != DMA_MAPPING_ERROR); } size_t virtio_max_dma_size(const struct virtio_device *vdev)@@ -366,7 +368,7 @@ static struct device *vring_dma_dev(const struct vring_virtqueue *vq) static int vring_map_one_sg(const struct vring_virtqueue *vq, struct scatterlist *sg, enum dma_data_direction direction, dma_addr_t *addr) { - if (vq->premapped) { + if (sg_is_premapped(sg)) { *addr = sg_dma_address(sg); return 0; }@@ -457,7 +459,7 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq, (flags & VRING_DESC_F_WRITE) ? DMA_FROM_DEVICE : DMA_TO_DEVICE); } else { - if (!vring_need_unmap_buffer(vq)) + if (!vring_need_unmap_buffer(vq, extra)) goto out; dma_unmap_page(vring_dma_dev(vq),@@ -510,7 +512,7 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq, dma_addr_t addr, unsigned int len, u16 flags, - bool indirect) + bool indirect, bool premapped) { u16 next;@@ -518,7 +520,7 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq, desc[i].addr = cpu_to_virtio64(vq->vdev, addr); desc[i].len = cpu_to_virtio32(vq->vdev, len); - extra[i].addr = addr; + extra[i].addr = premapped ? DMA_MAPPING_ERROR : addr; extra[i].len = len; extra[i].flags = flags;@@ -611,7 +613,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, */ i = virtqueue_add_desc_split(_vq, desc, extra, i, addr, sg->length, VRING_DESC_F_NEXT, - indirect); + indirect, sg_is_premapped(sg)); } } for (; n < (out_sgs + in_sgs); n++) {@@ -629,12 +631,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, sg->length, VRING_DESC_F_NEXT | VRING_DESC_F_WRITE, - indirect); + indirect, sg_is_premapped(sg)); } } /* Last one doesn't continue. */ desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); - if (!indirect && vring_need_unmap_buffer(vq)) + if (!indirect && vring_need_unmap_buffer(vq, &extra[prev])) vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &= ~VRING_DESC_F_NEXT;@@ -643,19 +645,15 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, dma_addr_t addr = vring_map_single( vq, desc, total_sg * sizeof(struct vring_desc), DMA_TO_DEVICE); - if (vring_mapping_error(vq, addr)) { - if (vq->premapped) - goto free_indirect; - + if (vring_mapping_error(vq, addr)) goto unmap_release; - } virtqueue_add_desc_split(_vq, vq->split.vring.desc, vq->split.desc_extra, head, addr, total_sg * sizeof(struct vring_desc), VRING_DESC_F_INDIRECT, - false); + false, false); } /* We're using some buffers from the free list. */@@ -712,7 +710,6 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, i = vring_unmap_one_split(vq, &extra[i]); } -free_indirect: if (indirect) kfree(desc);@@ -794,7 +791,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head, VRING_DESC_F_INDIRECT)); BUG_ON(len == 0 || len % sizeof(struct vring_desc)); - if (vring_need_unmap_buffer(vq)) { + if (vq->use_dma_api) { for (j = 0; j < len / sizeof(struct vring_desc); j++) vring_unmap_one_split(vq, &extra[j]); }@@ -1228,7 +1225,7 @@ static void vring_unmap_extra_packed(const struct vring_virtqueue *vq, (flags & VRING_DESC_F_WRITE) ? DMA_FROM_DEVICE : DMA_TO_DEVICE); } else { - if (!vring_need_unmap_buffer(vq)) + if (!vring_need_unmap_buffer(vq, extra)) return; dma_unmap_page(vring_dma_dev(vq),@@ -1309,7 +1306,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, i++; if (unlikely(vq->use_dma_api)) { - extra[i].addr = addr; + extra[i].addr = sg_is_premapped(sg) ? DMA_MAPPING_ERROR : addr; extra[i].len = sg->length; extra[i].flags = n < out_sgs ? 0 : VRING_DESC_F_WRITE; }@@ -1320,12 +1317,8 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, addr = vring_map_single(vq, desc, total_sg * sizeof(struct vring_packed_desc), DMA_TO_DEVICE); - if (vring_mapping_error(vq, addr)) { - if (vq->premapped) - goto free_desc; - + if (vring_mapping_error(vq, addr)) goto unmap_release; - } vq->packed.vring.desc[head].addr = cpu_to_le64(addr); vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *@@ -1383,7 +1376,6 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, for (i = 0; i < err_idx; i++) vring_unmap_extra_packed(vq, &extra[i]); -free_desc: kfree(desc); END_USE(vq);@@ -1474,7 +1466,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, desc[i].id = cpu_to_le16(id); if (unlikely(vq->use_dma_api)) { - vq->packed.desc_extra[curr].addr = addr; + vq->packed.desc_extra[curr].addr = sg_is_premapped(sg) ? + DMA_MAPPING_ERROR : addr; vq->packed.desc_extra[curr].len = sg->length; vq->packed.desc_extra[curr].flags = le16_to_cpu(flags);@@ -1625,10 +1618,9 @@ static void detach_buf_packed(struct vring_virtqueue *vq, if (!extra) return; - if (vring_need_unmap_buffer(vq)) { + if (vq->use_dma_api) { len = vq->packed.desc_extra[id].len; - for (i = 0; i < len / sizeof(struct vring_packed_desc); - i++) + for (i = 0; i < len / sizeof(struct vring_packed_desc); i++)
Unnecessary changes?
quoted hunk ↗ jump to hunk
vring_unmap_extra_packed(vq, &extra[i]); } kfree(desc);@@ -2212,6 +2204,11 @@ static inline int virtqueue_add(struct virtqueue *_vq, * @data: the token identifying the buffer. * @gfp: how to do memory allocations (if necessary). * + * When sg_page(sg) is NULL, this indicates that the driver has performed DMA + * mapping in advance, allowing the virtio core to directly utilize + * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally, + * DMA unmap operations for this buffer will be bypassed. + * * Caller must ensure we don't call this with other virtqueue operations * at the same time (except where noted). *@@ -2246,6 +2243,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_sgs); * @data: the token identifying the buffer. * @gfp: how to do memory allocations (if necessary). * + * When sg_page(sg) is NULL, this indicates that the driver has performed DMA + * mapping in advance, allowing the virtio core to directly utilize + * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally, + * DMA unmap operations for this buffer will be bypassed. + * * Caller must ensure we don't call this with other virtqueue operations * at the same time (except where noted). *@@ -2268,6 +2270,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_outbuf); * @data: the token identifying the buffer. * @gfp: how to do memory allocations (if necessary). * + * When sg_page(sg) is NULL, this indicates that the driver has performed DMA + * mapping in advance, allowing the virtio core to directly utilize + * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally, + * DMA unmap operations for this buffer will be bypassed. + * * Caller must ensure we don't call this with other virtqueue operations * at the same time (except where noted). *@@ -2291,6 +2298,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf); * @ctx: extra context for the token * @gfp: how to do memory allocations (if necessary). * + * When sg_page(sg) is NULL, this indicates that the driver has performed DMA + * mapping in advance, allowing the virtio core to directly utilize + * sg_dma_address(sg) without conducting any internal DMA mapping. Additionally, + * DMA unmap operations for this buffer will be bypassed. + * * Caller must ensure we don't call this with other virtqueue operations * at the same time (except where noted). * --2.32.0.3.g01195cf9f
Thanks