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 > > Cheers > Vladimir