Re: [PATCH 05/18] nvme-tcp: implement recvmsg rx flow for TLS

[Sagi Grimberg <sagi@grimberg.me>]

>> On 3/21/23 14:43, Hannes Reinecke wrote:
>>> TLS offload only implements recvmsg(), so implement the receive
>>> side with using recvmsg().
>>
>> I don't really mind changing this, however this change makes us
>> lock the socket for every consumption, instead of taking the lock
>> once and consume as much as possible. Which in theory is suboptimal.
>>
>> Is there any material reason why tls cannot implement read_sock() ?
>>
> Because the 'read_sock()' interface operates on skbs, but for TLS we 
> just have a 'stream' (there is this 'stream parser' thingie handling the 
> data), and skbs are meaningless as the decrypted payload can extend 
> across several skbs.
> At least, that's how I understood that.

I don't see why it can't produce an skb though...
Seems like there is a need here, because I don't know how we'd pass
a digest inline calculation to recvmsg. I'd hate to move the digest
calculation all the way up to the completion and rescan all the
data...

> But really, the prime reason is that I'm _far_ more familiar with the 
> NVMe code than the tls networking code, so implementing the recvmsg() 
> flow was relatively simple.
> 
> Maybe we can ask Boris Pismenny to implement read_sock() for tls ...

Maybe... CCing Boris.

> 
>>>
>>> Signed-off-by: Hannes Reinecke <hare@suse.de>
>>> ---
>>>   drivers/nvme/host/tcp.c | 156 ++++++++++++++++++++--------------------
>>>   1 file changed, 77 insertions(+), 79 deletions(-)
>>>
>>> diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
>>> index 42c0598c31f2..0e14b1b90855 100644
>>> --- a/drivers/nvme/host/tcp.c
>>> +++ b/drivers/nvme/host/tcp.c
>>> @@ -529,7 +529,7 @@ static void nvme_tcp_init_recv_ctx(struct 
>>> nvme_tcp_queue *queue)
>>>       queue->pdu_remaining = sizeof(struct nvme_tcp_rsp_pdu) +
>>>                   nvme_tcp_hdgst_len(queue);
>>>       queue->pdu_offset = 0;
>>> -    queue->data_remaining = -1;
>>> +    queue->data_remaining = 0;
>>>       queue->ddgst_remaining = 0;
>>>   }
>>> @@ -707,25 +707,32 @@ static int nvme_tcp_handle_r2t(struct 
>>> nvme_tcp_queue *queue,
>>>       return 0;
>>>   }
>>> -static int nvme_tcp_recv_pdu(struct nvme_tcp_queue *queue, struct 
>>> sk_buff *skb,
>>> -        unsigned int *offset, size_t *len)
>>> +static int nvme_tcp_recv_pdu(struct nvme_tcp_queue *queue, bool 
>>> pending)
>>>   {
>>>       struct nvme_tcp_hdr *hdr;
>>> -    char *pdu = queue->pdu;
>>> -    size_t rcv_len = min_t(size_t, *len, queue->pdu_remaining);
>>> +    size_t rcv_len = queue->pdu_remaining;
>>> +    struct msghdr msg = {
>>> +        .msg_flags = pending ? 0 : MSG_DONTWAIT,
>>
>> Umm, why?
>> What is the reason to block in this recv?
>>
> To avoid frequent -EAGAIN returns; that looked really ugly in the
> debug logs :-)
> Can try to do away with that; if we do also the 'pending' argument
> can be removed, so might be an idea.

I'd prefer not to block on any socket opreation, unless someone
shows that there is a gain to be made somehow.

> 
>>> +    };
>>> +    struct kvec iov = {
>>> +        .iov_base = (u8 *)queue->pdu + queue->pdu_offset,
>>> +        .iov_len = rcv_len,
>>> +    };
>>>       int ret;
>>> -    ret = skb_copy_bits(skb, *offset,
>>> -        &pdu[queue->pdu_offset], rcv_len);
>>> -    if (unlikely(ret))
>>> +    if (nvme_tcp_recv_state(queue) != NVME_TCP_RECV_PDU)
>>> +        return 0;
>>
>> Why is this check needed? looks like a left-over.
>>
> Yeah.
> 
>>> +
>>> +    ret = kernel_recvmsg(queue->sock, &msg, &iov, 1,
>>> +                 iov.iov_len, msg.msg_flags);
>>> +    if (ret <= 0)
>>>           return ret;
>>> +    rcv_len = ret;
>>>       queue->pdu_remaining -= rcv_len;
>>>       queue->pdu_offset += rcv_len;
>>> -    *offset += rcv_len;
>>> -    *len -= rcv_len;
>>>       if (queue->pdu_remaining)
>>> -        return 0;
>>> +        return queue->pdu_remaining;
>>>       hdr = queue->pdu;
>>>       if (queue->hdr_digest) {
>>> @@ -734,7 +741,6 @@ static int nvme_tcp_recv_pdu(struct 
>>> nvme_tcp_queue *queue, struct sk_buff *skb,
>>>               return ret;
>>>       }
>>> -
>>>       if (queue->data_digest) {
>>>           ret = nvme_tcp_check_ddgst(queue, queue->pdu);
>>>           if (unlikely(ret))
>>> @@ -765,19 +771,21 @@ static inline void nvme_tcp_end_request(struct 
>>> request *rq, u16 status)
>>>           nvme_complete_rq(rq);
>>>   }
>>> -static int nvme_tcp_recv_data(struct nvme_tcp_queue *queue, struct 
>>> sk_buff *skb,
>>> -                  unsigned int *offset, size_t *len)
>>> +static int nvme_tcp_recv_data(struct nvme_tcp_queue *queue)
>>>   {
>>>       struct nvme_tcp_data_pdu *pdu = (void *)queue->pdu;
>>>       struct request *rq =
>>>           nvme_cid_to_rq(nvme_tcp_tagset(queue), pdu->command_id);
>>>       struct nvme_tcp_request *req = blk_mq_rq_to_pdu(rq);
>>> +    if (nvme_tcp_recv_state(queue) != NVME_TCP_RECV_DATA)
>>> +        return 0;
>>> +
>>>       while (true) {
>>> -        int recv_len, ret;
>>> +        struct msghdr msg;
>>> +        int ret;
>>> -        recv_len = min_t(size_t, *len, queue->data_remaining);
>>> -        if (!recv_len)
>>> +        if (!queue->data_remaining)
>>>               break;
>>>           if (!iov_iter_count(&req->iter)) {
>>> @@ -798,25 +806,20 @@ static int nvme_tcp_recv_data(struct 
>>> nvme_tcp_queue *queue, struct sk_buff *skb,
>>>           }
>>>           /* we can read only from what is left in this bio */
>>> -        recv_len = min_t(size_t, recv_len,
>>> -                iov_iter_count(&req->iter));
>>> +        memset(&msg, 0, sizeof(msg));
>>> +        msg.msg_iter = req->iter;
>>> -        if (queue->data_digest)
>>> -            ret = skb_copy_and_hash_datagram_iter(skb, *offset,
>>> -                &req->iter, recv_len, queue->rcv_hash);
>>> -        else
>>> -            ret = skb_copy_datagram_iter(skb, *offset,
>>> -                    &req->iter, recv_len);
>>> -        if (ret) {
>>> +        ret = sock_recvmsg(queue->sock, &msg, 0);
>>
>> Who updates the rcv_hash for data digest validation?
>>
> Weelll ... currently, no-one.
> One of the things which I haven't tested.

I see, that obviously needs to work. This is primarily why
I want to have .read_sock for tls.

> 
>>> +        if (ret <= 0) {
>>>               dev_err(queue->ctrl->ctrl.device,
>>> -                "queue %d failed to copy request %#x data",
>>> +                "queue %d failed to receive request %#x data",
>>>                   nvme_tcp_queue_id(queue), rq->tag);
>>>               return ret;
>>>           }
>>> -        *len -= recv_len;
>>> -        *offset += recv_len;
>>> -        queue->data_remaining -= recv_len;
>>> +        queue->data_remaining -= ret;
>>> +        if (queue->data_remaining)
>>> +            nvme_tcp_advance_req(req, ret);
>>>       }
>>>       if (!queue->data_remaining) {
>>> @@ -833,27 +836,36 @@ static int nvme_tcp_recv_data(struct 
>>> nvme_tcp_queue *queue, struct sk_buff *skb,
>>>           }
>>>       }
>>> -    return 0;
>>> +    return queue->data_remaining;
>>>   }
>>> -static int nvme_tcp_recv_ddgst(struct nvme_tcp_queue *queue,
>>> -        struct sk_buff *skb, unsigned int *offset, size_t *len)
>>> +static int nvme_tcp_recv_ddgst(struct nvme_tcp_queue *queue)
>>>   {
>>>       struct nvme_tcp_data_pdu *pdu = (void *)queue->pdu;
>>>       char *ddgst = (char *)&queue->recv_ddgst;
>>> -    size_t recv_len = min_t(size_t, *len, queue->ddgst_remaining);
>>> +    size_t recv_len = queue->ddgst_remaining;
>>>       off_t off = NVME_TCP_DIGEST_LENGTH - queue->ddgst_remaining;
>>> +    struct msghdr msg = {
>>> +        .msg_flags = 0,
>>> +    };
>>> +    struct kvec iov = {
>>> +        .iov_base = (u8 *)ddgst + off,
>>> +        .iov_len = recv_len,
>>> +    };
>>>       int ret;
>>> -    ret = skb_copy_bits(skb, *offset, &ddgst[off], recv_len);
>>> -    if (unlikely(ret))
>>> +    if (nvme_tcp_recv_state(queue) != NVME_TCP_RECV_DDGST)
>>> +        return 0;
>>> +
>>> +    ret = kernel_recvmsg(queue->sock, &msg, &iov, 1, iov.iov_len,
>>> +                 msg.msg_flags);
>>> +    if (ret <= 0)
>>>           return ret;
>>> +    recv_len = ret;
>>>       queue->ddgst_remaining -= recv_len;
>>> -    *offset += recv_len;
>>> -    *len -= recv_len;
>>>       if (queue->ddgst_remaining)
>>> -        return 0;
>>> +        return queue->ddgst_remaining;
>>>       if (queue->recv_ddgst != queue->exp_ddgst) {
>>>           struct request *rq = nvme_cid_to_rq(nvme_tcp_tagset(queue),
>>> @@ -881,37 +893,41 @@ static int nvme_tcp_recv_ddgst(struct 
>>> nvme_tcp_queue *queue,
>>>       return 0;
>>>   }
>>> -static int nvme_tcp_recv_skb(read_descriptor_t *desc, struct sk_buff 
>>> *skb,
>>> -                 unsigned int offset, size_t len)
>>> +static int nvme_tcp_try_recv(struct nvme_tcp_queue *queue, bool 
>>> pending)
>>>   {
>>> -    struct nvme_tcp_queue *queue = desc->arg.data;
>>> -    size_t consumed = len;
>>>       int result;
>>> +    int nr_cqe = queue->nr_cqe;
>>> -    while (len) {
>>> +    do {
>>>           switch (nvme_tcp_recv_state(queue)) {
>>>           case NVME_TCP_RECV_PDU:
>>> -            result = nvme_tcp_recv_pdu(queue, skb, &offset, &len);
>>> -            break;
>>> +            result = nvme_tcp_recv_pdu(queue, pending);
>>> +            if (result)
>>> +                break;
>>> +            fallthrough;
>>>           case NVME_TCP_RECV_DATA:
>>> -            result = nvme_tcp_recv_data(queue, skb, &offset, &len);
>>> -            break;
>>> +            result = nvme_tcp_recv_data(queue);
>>> +            if (result)
>>> +                break;
>>> +            fallthrough;
>>>           case NVME_TCP_RECV_DDGST:
>>> -            result = nvme_tcp_recv_ddgst(queue, skb, &offset, &len);
>>> +            result = nvme_tcp_recv_ddgst(queue);
>>>               break;
>>>           default:
>>>               result = -EFAULT;
>>>           }
>>> -        if (result) {
>>> -            dev_err(queue->ctrl->ctrl.device,
>>> -                "receive failed:  %d\n", result);
>>> -            queue->rd_enabled = false;
>>> -            nvme_tcp_error_recovery(&queue->ctrl->ctrl);
>>> -            return result;
>>> -        }
>>> +        if (nr_cqe != queue->nr_cqe)
>>> +            break;
>>> +    } while (result >= 0);
>>> +    if (result < 0 && result != -EAGAIN) {
>>> +        dev_err(queue->ctrl->ctrl.device,
>>> +            "receive failed: %d state %d %s\n",
>>> +            result, nvme_tcp_recv_state(queue),
>>> +            pending ? "pending" : "");
>>
>> I'm unclear why pending would be an input to try_recv. Semantically
>> it is an output, signalling the io_work that data is pending to be
>> reaped from the socket.
>>
> See above. 'pending' is really there to clear the 'NOWAIT' flag for 
> recvmsg(), and to avoid frequent -EAGAIN returns.
> If we're fine handling them it can be removed.

I think we can remove it for now, it will also simplify the code.