On 8/3/22 13:55, Michael S. Tsirkin wrote:
> On Wed, Aug 03, 2022 at 01:25:15PM +0100, Vladimir Murzin wrote:
>> On 8/3/22 12:39, Michael S. Tsirkin wrote:
>>> On Wed, Aug 03, 2022 at 09:57:35AM +0100, Vladimir Murzin wrote:
>>>> On 8/2/22 13:49, Vladimir Murzin wrote:
>>>>> Hi Laurent,
>>>>>
>>>>> On 10/28/21 11:11, Laurent Vivier wrote:
>>>>>> If we ensure we have already some data available by enqueuing
>>>>>> again the buffer once data are exhausted, we can return what we
>>>>>> have without waiting for the device answer.
>>>>>>
>>>>>> Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx>
>>>>>> ---
>>>>>> drivers/char/hw_random/virtio-rng.c | 26 ++++++++++++--------------
>>>>>> 1 file changed, 12 insertions(+), 14 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
>>>>>> index 8ba97cf4ca8f..0a7dde135db1 100644
>>>>>> --- a/drivers/char/hw_random/virtio-rng.c
>>>>>> +++ b/drivers/char/hw_random/virtio-rng.c
>>>>>> @@ -20,7 +20,6 @@ struct virtrng_info {
>>>>>> struct virtqueue *vq;
>>>>>> char name[25];
>>>>>> int index;
>>>>>> - bool busy;
>>>>>> bool hwrng_register_done;
>>>>>> bool hwrng_removed;
>>>>>> /* data transfer */
>>>>>> @@ -44,16 +43,18 @@ static void random_recv_done(struct virtqueue *vq)
>>>>>> return;
>>>>>>
>>>>>> vi->data_idx = 0;
>>>>>> - vi->busy = false;
>>>>>>
>>>>>> complete(&vi->have_data);
>>>>>> }
>>>>>>
>>>>>> -/* The host will fill any buffer we give it with sweet, sweet randomness. */
>>>>>> -static void register_buffer(struct virtrng_info *vi)
>>>>>> +static void request_entropy(struct virtrng_info *vi)
>>>>>> {
>>>>>> struct scatterlist sg;
>>>>>>
>>>>>> + reinit_completion(&vi->have_data);
>>>>>> + vi->data_avail = 0;
>>>>>> + vi->data_idx = 0;
>>>>>> +
>>>>>> sg_init_one(&sg, vi->data, sizeof(vi->data));
>>>>>>
>>>>>> /* There should always be room for one buffer. */
>>>>>> @@ -69,6 +70,8 @@ static unsigned int copy_data(struct virtrng_info *vi, void *buf,
>>>>>> memcpy(buf, vi->data + vi->data_idx, size);
>>>>>> vi->data_idx += size;
>>>>>> vi->data_avail -= size;
>>>>>> + if (vi->data_avail == 0)
>>>>>> + request_entropy(vi);
>>>>>> return size;
>>>>>> }
>>>>>>
>>>>>> @@ -98,13 +101,7 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
>>>>>> * so either size is 0 or data_avail is 0
>>>>>> */
>>>>>> while (size != 0) {
>>>>>> - /* data_avail is 0 */
>>>>>> - if (!vi->busy) {
>>>>>> - /* no pending request, ask for more */
>>>>>> - vi->busy = true;
>>>>>> - reinit_completion(&vi->have_data);
>>>>>> - register_buffer(vi);
>>>>>> - }
>>>>>> + /* data_avail is 0 but a request is pending */
>>>>>> ret = wait_for_completion_killable(&vi->have_data);
>>>>>> if (ret < 0)
>>>>>> return ret;
>>>>>> @@ -126,8 +123,7 @@ static void virtio_cleanup(struct hwrng *rng)
>>>>>> {
>>>>>> struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
>>>>>>
>>>>>> - if (vi->busy)
>>>>>> - complete(&vi->have_data);
>>>>>> + complete(&vi->have_data);
>>>>>> }
>>>>>>
>>>>>> static int probe_common(struct virtio_device *vdev)
>>>>>> @@ -163,6 +159,9 @@ static int probe_common(struct virtio_device *vdev)
>>>>>> goto err_find;
>>>>>> }
>>>>>>
>>>>>> + /* we always have a pending entropy request */
>>>>>> + request_entropy(vi);
>>>>>> +
>>>>>> return 0;
>>>>>>
>>>>>> err_find:
>>>>>> @@ -181,7 +180,6 @@ static void remove_common(struct virtio_device *vdev)
>>>>>> vi->data_idx = 0;
>>>>>> complete(&vi->have_data);
>>>>>> vdev->config->reset(vdev);
>>>>>> - vi->busy = false;
>>>>>> if (vi->hwrng_register_done)
>>>>>> hwrng_unregister(&vi->hwrng);
>>>>>> vdev->config->del_vqs(vdev);
>>>>>
>>>>> We observed that after this commit virtio-rng implementation in FVP doesn't
>>>>> work
>>>>>
>>>>> INFO: bp.virtio_rng: Selected Random Generator Device: XORSHIFT DEVICE
>>>>> INFO: bp.virtio_rng: Using seed value: 0x5674bba8
>>>>> Error: FVP_Base_AEMvA: bp.virtio_rng: <vq0-requestq> Found invalid descriptor index
>>>>> In file: (unknown):0
>>>>> In process: FVP_Base_AEMvA.thread_p_12 @ 935500020 ns
>>>>> Info: FVP_Base_AEMvA: bp.virtio_rng: Could not extract buffer
>>>>>
>>>>> while basic baremetal test works as expected
>>>>>
>>>>> INFO: bp.virtio_rng: Selected Random Generator Device: XORSHIFT DEVICE
>>>>> INFO: bp.virtio_rng: Using seed value: 0x541c142e
>>>>> Info: FVP_Base_AEMv8A: bp.virtio_rng: Generated Number: 0x4b098991ceb377e6
>>>>> Info: FVP_Base_AEMv8A: bp.virtio_rng: Generated Number: 0xbdcbe3f765ba62f7
>>>>>
>>>>> We are trying to get an idea what is missing and where, yet none of us familiar
>>>>> with the driver :(
>>>>>
>>>>> I'm looping Kevin who originally reported that and Mauricio who is looking form
>>>>> the FVP side.
>>>>
>>>> With the following diff FVP works agin
>>>>
>>>> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
>>>> index a6f3a8a2ac..042503ad6c 100644
>>>> --- a/drivers/char/hw_random/virtio-rng.c
>>>> +++ b/drivers/char/hw_random/virtio-rng.c
>>>> @@ -54,6 +54,7 @@ static void request_entropy(struct virtrng_info *vi)
>>>> reinit_completion(&vi->have_data);
>>>> vi->data_avail = 0;
>>>> vi->data_idx = 0;
>>>> + smp_mb();
>>>>
>>>> sg_init_one(&sg, vi->data, sizeof(vi->data));
>>>>
>>>>
>>>> What do you reckon?
>>>>
>>>> Cheers
>>>> Vladimir
>>>
>>> Thanks for debugging this!
>>>
>>> OK, interesting.
>>>
>>> data_idx and data_avail are accessed from virtio_read.
>>>
>>> Which as far as I can tell is invoked just with reading_mutex.
>>>
>>>
>>> But, request_entropy is called from probe when device is registered
>>> this time without locks
>>> so it can trigger while another thread is calling virtio_read.
>>>
>>> Second request_entropy is called from a callback random_recv_done
>>> also without locks.
>>>
>>> So it's great that smp_mb helped here but I suspect in fact we
>>> need locking. Laurent?
>>>
>>
>> I'm sorry for the noise, but it looks like I'm seeing issue for some different reasons.
>> I manage to reproduce issue even with smb_mb() in place. The reason I though it helped
>> is because I changed both environment and added smb_mb().
>>
>> Anyway, thank you for your time!
>>
>> Cheers
>> Vladimir
>
> Well we at least have a race condition found by code review here. Here's
> a quick hack attempting to fix it. I don't like it much since
> it adds buffers with GFP_ATOMIC and kicks under a spinlock, but
> for now we can at least test it. I did a quick build but that's
> all, a bit rushed now sorry. Would appreciate knowing whether
> this addresses the issue for you.
>
>
> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
> index a6f3a8a2aca6..36121c8d0315 100644
> --- a/drivers/char/hw_random/virtio-rng.c
> +++ b/drivers/char/hw_random/virtio-rng.c
> @@ -23,6 +23,7 @@ struct virtrng_info {
> bool hwrng_register_done;
> bool hwrng_removed;
> /* data transfer */
> + spinlock_t lock;
> struct completion have_data;
> unsigned int data_avail;
> unsigned int data_idx;
> @@ -37,6 +38,9 @@ struct virtrng_info {
> static void random_recv_done(struct virtqueue *vq)
> {
> struct virtrng_info *vi = vq->vdev->priv;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&vi->lock, flags);
>
> /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
> if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
> @@ -45,20 +49,20 @@ static void random_recv_done(struct virtqueue *vq)
> vi->data_idx = 0;
>
> complete(&vi->have_data);
> + spin_unlock_irqrestore(&vi->lock, flags);
> }
>
> static void request_entropy(struct virtrng_info *vi)
> {
> struct scatterlist sg;
>
> - reinit_completion(&vi->have_data);
> - vi->data_avail = 0;
> + BUG_ON(vi->data_avail != 0);
> vi->data_idx = 0;
>
> sg_init_one(&sg, vi->data, sizeof(vi->data));
>
> /* There should always be room for one buffer. */
> - virtqueue_add_inbuf(vi->vq, &sg, 1, vi->data, GFP_KERNEL);
> + virtqueue_add_inbuf(vi->vq, &sg, 1, vi->data, GFP_ATOMIC);
>
> virtqueue_kick(vi->vq);
> }
> @@ -70,8 +74,10 @@ static unsigned int copy_data(struct virtrng_info *vi, void *buf,
> memcpy(buf, vi->data + vi->data_idx, size);
> vi->data_idx += size;
> vi->data_avail -= size;
> - if (vi->data_avail == 0)
> + if (vi->data_avail == 0) {
> + reinit_completion(&vi->have_data);
> request_entropy(vi);
> + }
> return size;
> }
>
> @@ -81,18 +87,21 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
> struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
> unsigned int chunk;
> size_t read;
> + unsigned long flags;
>
> if (vi->hwrng_removed)
> return -ENODEV;
>
> read = 0;
>
> + spin_lock_irqsave(&vi->lock, flags);
> /* copy available data */
> if (vi->data_avail) {
> chunk = copy_data(vi, buf, size);
> size -= chunk;
> read += chunk;
> }
> + spin_unlock_irqrestore(&vi->lock, flags);
>
> if (!wait)
> return read;
> @@ -108,12 +117,14 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
> /* if vi->data_avail is 0, we have been interrupted
> * by a cleanup, but buffer stays in the queue
> */
> + spin_lock_irqsave(&vi->lock, flags);
> if (vi->data_avail == 0)
> return read;
>
> chunk = copy_data(vi, buf + read, size);
> size -= chunk;
> read += chunk;
> + spin_unlock_irqrestore(&vi->lock, flags);
> }
>
> return read;
> @@ -122,19 +133,25 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
> static void virtio_cleanup(struct hwrng *rng)
> {
> struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
> + unsigned long flags;
>
> + spin_lock_irqsave(&vi->lock, flags);
> complete(&vi->have_data);
> + spin_unlock_irqrestore(&vi->lock, flags);
> }
>
> static int probe_common(struct virtio_device *vdev)
> {
> int err, index;
> struct virtrng_info *vi = NULL;
> + unsigned long flags;
>
> vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
> if (!vi)
> return -ENOMEM;
>
> + spin_lock_init(&vi->lock);
> +
> vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
> if (index < 0) {
> err = index;
> @@ -162,7 +179,10 @@ static int probe_common(struct virtio_device *vdev)
> virtio_device_ready(vdev);
>
> /* we always have a pending entropy request */
> - request_entropy(vi);
> + spin_lock_irqsave(&vi->lock, flags);
> + if (vi->data_avail == 0)
> + request_entropy(vi);
> + spin_unlock_irqrestore(&vi->lock, flags);
>
> return 0;
>
>
Thanks a lot! I gave it a go and it did not help. I think I need to find out how exactly
my environment affected... it not necessary need to be kernel related.
Cheers
Vladimir
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