* [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
@ 2024-09-04 6:10 Wenbo Li
2024-09-04 6:31 ` Jason Wang
2024-09-04 6:45 ` Xuan Zhuo
0 siblings, 2 replies; 6+ messages in thread
From: Wenbo Li @ 2024-09-04 6:10 UTC (permalink / raw)
To: mst, jasowang, xuanzhuo, eperezma, davem, edumazet, kuba, pabeni
Cc: virtualization, netdev, linux-kernel, Wenbo Li, Jiahui Cen,
Ying Fang
Currently, the virtio-net driver will perform a pre-dma-mapping for
small or mergeable RX buffer. But for small packets, a mismatched address
without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
That will result in unsynchronized buffers when SWIOTLB is enabled, for
example, when running as a TDX guest.
This patch handles small and mergeable packets separately and fixes
the mismatched buffer address.
Changes from v1: Use ctx to get xdp_headroom.
Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling mergeable buffers")
Signed-off-by: Wenbo Li <liwenbo.martin@bytedance.com>
Signed-off-by: Jiahui Cen <cenjiahui@bytedance.com>
Signed-off-by: Ying Fang <fangying.tommy@bytedance.com>
---
drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c6af18948..cbc3c0ae4 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
return buf;
}
+static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
+ u32 *len,
+ void **ctx,
+ unsigned int header_offset)
+{
+ void *buf;
+ unsigned int xdp_headroom;
+
+ buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
+ if (buf) {
+ xdp_headroom = (unsigned long)*ctx;
+ virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom, *len);
+ }
+
+ return buf;
+}
+
static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
{
struct virtnet_rq_dma *dma;
@@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct virtnet_info *vi,
int packets = 0;
void *buf;
- if (!vi->big_packets || vi->mergeable_rx_bufs) {
+ if (vi->mergeable_rx_bufs) {
void *ctx;
while (packets < budget &&
(buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
packets++;
}
+ } else if (!vi->big_packets) {
+ void *ctx;
+ unsigned int xdp_headroom = virtnet_get_headroom(vi);
+ unsigned int header_offset = VIRTNET_RX_PAD + xdp_headroom;
+
+ while (packets < budget &&
+ (buf = virtnet_rq_get_buf_small(rq, &len, &ctx, header_offset))) {
+ receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
+ packets++;
+ }
} else {
while (packets < budget &&
(buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
--
2.20.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
2024-09-04 6:10 [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets Wenbo Li
@ 2024-09-04 6:31 ` Jason Wang
2024-09-04 6:45 ` Xuan Zhuo
1 sibling, 0 replies; 6+ messages in thread
From: Jason Wang @ 2024-09-04 6:31 UTC (permalink / raw)
To: Wenbo Li
Cc: mst, xuanzhuo, eperezma, davem, edumazet, kuba, pabeni,
virtualization, netdev, linux-kernel, Jiahui Cen, Ying Fang
On Wed, Sep 4, 2024 at 2:10 PM Wenbo Li <liwenbo.martin@bytedance.com> wrote:
>
> Currently, the virtio-net driver will perform a pre-dma-mapping for
> small or mergeable RX buffer. But for small packets, a mismatched address
> without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
>
> That will result in unsynchronized buffers when SWIOTLB is enabled, for
> example, when running as a TDX guest.
>
> This patch handles small and mergeable packets separately and fixes
> the mismatched buffer address.
>
> Changes from v1: Use ctx to get xdp_headroom.
>
> Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling mergeable buffers")
> Signed-off-by: Wenbo Li <liwenbo.martin@bytedance.com>
> Signed-off-by: Jiahui Cen <cenjiahui@bytedance.com>
> Signed-off-by: Ying Fang <fangying.tommy@bytedance.com>
> ---
> drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
> 1 file changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c6af18948..cbc3c0ae4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
> return buf;
> }
>
> +static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
> + u32 *len,
> + void **ctx,
> + unsigned int header_offset)
header_offset is unused?
> +{
> + void *buf;
> + unsigned int xdp_headroom;
> +
> + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> + if (buf) {
> + xdp_headroom = (unsigned long)*ctx;
> + virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom, *len);
> + }
> +
> + return buf;
> +}
> +
> static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> {
> struct virtnet_rq_dma *dma;
> @@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct virtnet_info *vi,
> int packets = 0;
> void *buf;
>
> - if (!vi->big_packets || vi->mergeable_rx_bufs) {
> + if (vi->mergeable_rx_bufs) {
> void *ctx;
> while (packets < budget &&
> (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
> packets++;
> }
> + } else if (!vi->big_packets) {
> + void *ctx;
> + unsigned int xdp_headroom = virtnet_get_headroom(vi);
> + unsigned int header_offset = VIRTNET_RX_PAD + xdp_headroom;
> +
> + while (packets < budget &&
> + (buf = virtnet_rq_get_buf_small(rq, &len, &ctx, header_offset))) {
> + receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
> + packets++;
> + }
> } else {
> while (packets < budget &&
> (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> --
> 2.20.1
>
Thanks
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
2024-09-04 6:10 [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets Wenbo Li
2024-09-04 6:31 ` Jason Wang
@ 2024-09-04 6:45 ` Xuan Zhuo
[not found] ` <CABwj4+hMwUQ+=m+XyG=66e+PUbOzOvHEsQzboB17DE+3aBHA3g@mail.gmail.com>
1 sibling, 1 reply; 6+ messages in thread
From: Xuan Zhuo @ 2024-09-04 6:45 UTC (permalink / raw)
To: Wenbo Li
Cc: virtualization, netdev, linux-kernel, Wenbo Li, Jiahui Cen,
Ying Fang, mst, jasowang, eperezma, davem, edumazet, kuba, pabeni
On Wed, 4 Sep 2024 14:10:09 +0800, Wenbo Li <liwenbo.martin@bytedance.com> wrote:
> Currently, the virtio-net driver will perform a pre-dma-mapping for
> small or mergeable RX buffer. But for small packets, a mismatched address
> without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
Will used virt_to_head_page(), so could you say more about it?
struct page *page = virt_to_head_page(buf);
Thanks.
>
> That will result in unsynchronized buffers when SWIOTLB is enabled, for
> example, when running as a TDX guest.
>
> This patch handles small and mergeable packets separately and fixes
> the mismatched buffer address.
>
> Changes from v1: Use ctx to get xdp_headroom.
>
> Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling mergeable buffers")
> Signed-off-by: Wenbo Li <liwenbo.martin@bytedance.com>
> Signed-off-by: Jiahui Cen <cenjiahui@bytedance.com>
> Signed-off-by: Ying Fang <fangying.tommy@bytedance.com>
> ---
> drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
> 1 file changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c6af18948..cbc3c0ae4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
> return buf;
> }
>
> +static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
> + u32 *len,
> + void **ctx,
> + unsigned int header_offset)
> +{
> + void *buf;
> + unsigned int xdp_headroom;
> +
> + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> + if (buf) {
> + xdp_headroom = (unsigned long)*ctx;
> + virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom, *len);
> + }
> +
> + return buf;
> +}
> +
> static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> {
> struct virtnet_rq_dma *dma;
> @@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct virtnet_info *vi,
> int packets = 0;
> void *buf;
>
> - if (!vi->big_packets || vi->mergeable_rx_bufs) {
> + if (vi->mergeable_rx_bufs) {
> void *ctx;
> while (packets < budget &&
> (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
> packets++;
> }
> + } else if (!vi->big_packets) {
> + void *ctx;
> + unsigned int xdp_headroom = virtnet_get_headroom(vi);
> + unsigned int header_offset = VIRTNET_RX_PAD + xdp_headroom;
> +
> + while (packets < budget &&
> + (buf = virtnet_rq_get_buf_small(rq, &len, &ctx, header_offset))) {
> + receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
> + packets++;
> + }
> } else {
> while (packets < budget &&
> (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> --
> 2.20.1
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [External] Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
[not found] ` <CABwj4+hMwUQ+=m+XyG=66e+PUbOzOvHEsQzboB17DE+3aBHA3g@mail.gmail.com>
@ 2024-09-04 7:30 ` Xuan Zhuo
2024-09-04 7:51 ` Wenbo Li
2024-09-04 10:57 ` Michael S. Tsirkin
0 siblings, 2 replies; 6+ messages in thread
From: Xuan Zhuo @ 2024-09-04 7:30 UTC (permalink / raw)
To: 文博李
Cc: virtualization, netdev, linux-kernel, Jiahui Cen, Ying Fang, mst,
jasowang, eperezma, davem, edumazet, kuba, pabeni
On Wed, 4 Sep 2024 15:21:28 +0800, =?utf-8?b?5paH5Y2a5p2O?= <liwenbo.martin@bytedance.com> wrote:
> When SWIOTLB is enabled, a DMA map will allocate a bounce buffer for real
> DMA operations,
> and when unmapping, SWIOTLB copies the content in the bounce buffer to the
> driver-allocated
> buffer (the `buf` variable). Such copy only synchronizes data in the buffer
> range, not the whole page.
> So we should give the correct offset for DMA unmapping.
I see.
But I think we should pass the "correct" buf to virtio core as the "data" by
virtqueue_add_inbuf_ctx().
In the merge mode, we pass the pointer that points to the virtnet header.
In the small mode, we pass the pointer that points to the virtnet header - offset.
But this is not the only problem, we try to get the virtnet header by the buf
inside receive_buf(before receive_small).
flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
So I think it is time to unify the buf that passed to the virtio core into a
pointer pointed to the virtnet header.
Thanks.
>
> Thanks.
>
> On Wed, Sep 4, 2024 at 2:46 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > On Wed, 4 Sep 2024 14:10:09 +0800, Wenbo Li <liwenbo.martin@bytedance.com>
> wrote:
> > > Currently, the virtio-net driver will perform a pre-dma-mapping for
> > > small or mergeable RX buffer. But for small packets, a mismatched
> address
> > > without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
> >
> > Will used virt_to_head_page(), so could you say more about it?
> >
> > struct page *page = virt_to_head_page(buf);
> >
> > Thanks.
> >
> > >
> > > That will result in unsynchronized buffers when SWIOTLB is enabled, for
> > > example, when running as a TDX guest.
> > >
> > > This patch handles small and mergeable packets separately and fixes
> > > the mismatched buffer address.
> > >
> > > Changes from v1: Use ctx to get xdp_headroom.
> > >
> > > Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling
> mergeable buffers")
> > > Signed-off-by: Wenbo Li <liwenbo.martin@bytedance.com>
> > > Signed-off-by: Jiahui Cen <cenjiahui@bytedance.com>
> > > Signed-off-by: Ying Fang <fangying.tommy@bytedance.com>
> > > ---
> > > drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
> > > 1 file changed, 28 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index c6af18948..cbc3c0ae4 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct
> receive_queue *rq, u32 *len, void **ctx)
> > > return buf;
> > > }
> > >
> > > +static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
> > > + u32 *len,
> > > + void **ctx,
> > > + unsigned int header_offset)
> > > +{
> > > + void *buf;
> > > + unsigned int xdp_headroom;
> > > +
> > > + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > > + if (buf) {
> > > + xdp_headroom = (unsigned long)*ctx;
> > > + virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
> *len);
> > > + }
> > > +
> > > + return buf;
> > > +}
> > > +
> > > static void virtnet_rq_init_one_sg(struct receive_queue *rq, void
> *buf, u32 len)
> > > {
> > > struct virtnet_rq_dma *dma;
> > > @@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct
> virtnet_info *vi,
> > > int packets = 0;
> > > void *buf;
> > >
> > > - if (!vi->big_packets || vi->mergeable_rx_bufs) {
> > > + if (vi->mergeable_rx_bufs) {
> > > void *ctx;
> > > while (packets < budget &&
> > > (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> > > receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
> stats);
> > > packets++;
> > > }
> > > + } else if (!vi->big_packets) {
> > > + void *ctx;
> > > + unsigned int xdp_headroom = virtnet_get_headroom(vi);
> > > + unsigned int header_offset = VIRTNET_RX_PAD +
> xdp_headroom;
> > > +
> > > + while (packets < budget &&
> > > + (buf = virtnet_rq_get_buf_small(rq, &len, &ctx,
> header_offset))) {
> > > + receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
> stats);
> > > + packets++;
> > > + }
> > > } else {
> > > while (packets < budget &&
> > > (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> > > --
> > > 2.20.1
> > >
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [External] Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
2024-09-04 7:30 ` [External] " Xuan Zhuo
@ 2024-09-04 7:51 ` Wenbo Li
2024-09-04 10:57 ` Michael S. Tsirkin
1 sibling, 0 replies; 6+ messages in thread
From: Wenbo Li @ 2024-09-04 7:51 UTC (permalink / raw)
To: Xuan Zhuo
Cc: virtualization, netdev, linux-kernel, Jiahui Cen, Ying Fang, mst,
jasowang, eperezma, davem, edumazet, kuba, pabeni
Thank you. I'll fix these in v3.
On 9/4/24 15:30, Xuan Zhuo wrote:
> On Wed, 4 Sep 2024 15:21:28 +0800, =?utf-8?b?5paH5Y2a5p2O?= <liwenbo.martin@bytedance.com> wrote:
>> When SWIOTLB is enabled, a DMA map will allocate a bounce buffer for real
>> DMA operations,
>> and when unmapping, SWIOTLB copies the content in the bounce buffer to the
>> driver-allocated
>> buffer (the `buf` variable). Such copy only synchronizes data in the buffer
>> range, not the whole page.
>> So we should give the correct offset for DMA unmapping.
> I see.
>
> But I think we should pass the "correct" buf to virtio core as the "data" by
> virtqueue_add_inbuf_ctx().
>
> In the merge mode, we pass the pointer that points to the virtnet header.
> In the small mode, we pass the pointer that points to the virtnet header - offset.
>
> But this is not the only problem, we try to get the virtnet header by the buf
> inside receive_buf(before receive_small).
>
> flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
>
> So I think it is time to unify the buf that passed to the virtio core into a
> pointer pointed to the virtnet header.
>
> Thanks.
>
>
>> Thanks.
>>
>> On Wed, Sep 4, 2024 at 2:46 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>>> On Wed, 4 Sep 2024 14:10:09 +0800, Wenbo Li <liwenbo.martin@bytedance.com>
>> wrote:
>>>> Currently, the virtio-net driver will perform a pre-dma-mapping for
>>>> small or mergeable RX buffer. But for small packets, a mismatched
>> address
>>>> without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
>>> Will used virt_to_head_page(), so could you say more about it?
>>>
>>> struct page *page = virt_to_head_page(buf);
>>>
>>> Thanks.
>>>
>>>> That will result in unsynchronized buffers when SWIOTLB is enabled, for
>>>> example, when running as a TDX guest.
>>>>
>>>> This patch handles small and mergeable packets separately and fixes
>>>> the mismatched buffer address.
>>>>
>>>> Changes from v1: Use ctx to get xdp_headroom.
>>>>
>>>> Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling
>> mergeable buffers")
>>>> Signed-off-by: Wenbo Li <liwenbo.martin@bytedance.com>
>>>> Signed-off-by: Jiahui Cen <cenjiahui@bytedance.com>
>>>> Signed-off-by: Ying Fang <fangying.tommy@bytedance.com>
>>>> ---
>>>> drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
>>>> 1 file changed, 28 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>> index c6af18948..cbc3c0ae4 100644
>>>> --- a/drivers/net/virtio_net.c
>>>> +++ b/drivers/net/virtio_net.c
>>>> @@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct
>> receive_queue *rq, u32 *len, void **ctx)
>>>> return buf;
>>>> }
>>>>
>>>> +static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
>>>> + u32 *len,
>>>> + void **ctx,
>>>> + unsigned int header_offset)
>>>> +{
>>>> + void *buf;
>>>> + unsigned int xdp_headroom;
>>>> +
>>>> + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
>>>> + if (buf) {
>>>> + xdp_headroom = (unsigned long)*ctx;
>>>> + virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
>> *len);
>>>> + }
>>>> +
>>>> + return buf;
>>>> +}
>>>> +
>>>> static void virtnet_rq_init_one_sg(struct receive_queue *rq, void
>> *buf, u32 len)
>>>> {
>>>> struct virtnet_rq_dma *dma;
>>>> @@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct
>> virtnet_info *vi,
>>>> int packets = 0;
>>>> void *buf;
>>>>
>>>> - if (!vi->big_packets || vi->mergeable_rx_bufs) {
>>>> + if (vi->mergeable_rx_bufs) {
>>>> void *ctx;
>>>> while (packets < budget &&
>>>> (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
>>>> receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
>> stats);
>>>> packets++;
>>>> }
>>>> + } else if (!vi->big_packets) {
>>>> + void *ctx;
>>>> + unsigned int xdp_headroom = virtnet_get_headroom(vi);
>>>> + unsigned int header_offset = VIRTNET_RX_PAD +
>> xdp_headroom;
>>>> +
>>>> + while (packets < budget &&
>>>> + (buf = virtnet_rq_get_buf_small(rq, &len, &ctx,
>> header_offset))) {
>>>> + receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
>> stats);
>>>> + packets++;
>>>> + }
>>>> } else {
>>>> while (packets < budget &&
>>>> (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
>>>> --
>>>> 2.20.1
>>>>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [External] Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
2024-09-04 7:30 ` [External] " Xuan Zhuo
2024-09-04 7:51 ` Wenbo Li
@ 2024-09-04 10:57 ` Michael S. Tsirkin
1 sibling, 0 replies; 6+ messages in thread
From: Michael S. Tsirkin @ 2024-09-04 10:57 UTC (permalink / raw)
To: Xuan Zhuo
Cc: 文博李, virtualization, netdev, linux-kernel,
Jiahui Cen, Ying Fang, jasowang, eperezma, davem, edumazet, kuba,
pabeni
On Wed, Sep 04, 2024 at 03:30:02PM +0800, Xuan Zhuo wrote:
> On Wed, 4 Sep 2024 15:21:28 +0800, =?utf-8?b?5paH5Y2a5p2O?= <liwenbo.martin@bytedance.com> wrote:
> > When SWIOTLB is enabled, a DMA map will allocate a bounce buffer for real
> > DMA operations,
> > and when unmapping, SWIOTLB copies the content in the bounce buffer to the
> > driver-allocated
> > buffer (the `buf` variable). Such copy only synchronizes data in the buffer
> > range, not the whole page.
> > So we should give the correct offset for DMA unmapping.
>
> I see.
>
> But I think we should pass the "correct" buf to virtio core as the "data" by
> virtqueue_add_inbuf_ctx().
>
> In the merge mode, we pass the pointer that points to the virtnet header.
> In the small mode, we pass the pointer that points to the virtnet header - offset.
>
> But this is not the only problem, we try to get the virtnet header by the buf
> inside receive_buf(before receive_small).
>
> flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
>
> So I think it is time to unify the buf that passed to the virtio core into a
> pointer pointed to the virtnet header.
>
> Thanks.
Hard to say without seeing what is proposed, but I think
data pointer is opaque to virtio, it does not have to
point to anything specific - just !NULL.
>
> >
> > Thanks.
> >
> > On Wed, Sep 4, 2024 at 2:46 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > On Wed, 4 Sep 2024 14:10:09 +0800, Wenbo Li <liwenbo.martin@bytedance.com>
> > wrote:
> > > > Currently, the virtio-net driver will perform a pre-dma-mapping for
> > > > small or mergeable RX buffer. But for small packets, a mismatched
> > address
> > > > without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
> > >
> > > Will used virt_to_head_page(), so could you say more about it?
> > >
> > > struct page *page = virt_to_head_page(buf);
> > >
> > > Thanks.
> > >
> > > >
> > > > That will result in unsynchronized buffers when SWIOTLB is enabled, for
> > > > example, when running as a TDX guest.
> > > >
> > > > This patch handles small and mergeable packets separately and fixes
> > > > the mismatched buffer address.
> > > >
> > > > Changes from v1: Use ctx to get xdp_headroom.
> > > >
> > > > Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling
> > mergeable buffers")
> > > > Signed-off-by: Wenbo Li <liwenbo.martin@bytedance.com>
> > > > Signed-off-by: Jiahui Cen <cenjiahui@bytedance.com>
> > > > Signed-off-by: Ying Fang <fangying.tommy@bytedance.com>
> > > > ---
> > > > drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
> > > > 1 file changed, 28 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index c6af18948..cbc3c0ae4 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct
> > receive_queue *rq, u32 *len, void **ctx)
> > > > return buf;
> > > > }
> > > >
> > > > +static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
> > > > + u32 *len,
> > > > + void **ctx,
> > > > + unsigned int header_offset)
> > > > +{
> > > > + void *buf;
> > > > + unsigned int xdp_headroom;
> > > > +
> > > > + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > > > + if (buf) {
> > > > + xdp_headroom = (unsigned long)*ctx;
> > > > + virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
> > *len);
> > > > + }
> > > > +
> > > > + return buf;
> > > > +}
> > > > +
> > > > static void virtnet_rq_init_one_sg(struct receive_queue *rq, void
> > *buf, u32 len)
> > > > {
> > > > struct virtnet_rq_dma *dma;
> > > > @@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct
> > virtnet_info *vi,
> > > > int packets = 0;
> > > > void *buf;
> > > >
> > > > - if (!vi->big_packets || vi->mergeable_rx_bufs) {
> > > > + if (vi->mergeable_rx_bufs) {
> > > > void *ctx;
> > > > while (packets < budget &&
> > > > (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> > > > receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
> > stats);
> > > > packets++;
> > > > }
> > > > + } else if (!vi->big_packets) {
> > > > + void *ctx;
> > > > + unsigned int xdp_headroom = virtnet_get_headroom(vi);
> > > > + unsigned int header_offset = VIRTNET_RX_PAD +
> > xdp_headroom;
> > > > +
> > > > + while (packets < budget &&
> > > > + (buf = virtnet_rq_get_buf_small(rq, &len, &ctx,
> > header_offset))) {
> > > > + receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
> > stats);
> > > > + packets++;
> > > > + }
> > > > } else {
> > > > while (packets < budget &&
> > > > (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> > > > --
> > > > 2.20.1
> > > >
> >
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2024-09-04 10:57 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2024-09-04 6:10 [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets Wenbo Li
2024-09-04 6:31 ` Jason Wang
2024-09-04 6:45 ` Xuan Zhuo
[not found] ` <CABwj4+hMwUQ+=m+XyG=66e+PUbOzOvHEsQzboB17DE+3aBHA3g@mail.gmail.com>
2024-09-04 7:30 ` [External] " Xuan Zhuo
2024-09-04 7:51 ` Wenbo Li
2024-09-04 10:57 ` Michael S. Tsirkin
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).