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 <[email protected]> > >> --- > >> 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? -- MST _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
