linux-kernel - Re: [PATCH] rpmsg: virtio: Fix broken rpmsg

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Date:   Thu, 30 Jun 2022 18:20:19 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Anup Patel <apatel@...tanamicro.com>
CC:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Atish Patra <atishp@...shpatra.org>,
        Alistair Francis <Alistair.Francis@....com>,
        Anup Patel <anup@...infault.org>,
        <linux-remoteproc@...r.kernel.org>,
        <kvm-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rpmsg: virtio: Fix broken rpmsg_probe()

Hi,

On 6/29/22 19:43, Mathieu Poirier wrote:
> Hi Anup,
> 
> On Wed, Jun 08, 2022 at 10:43:34PM +0530, Anup Patel wrote:
>> The rpmsg_probe() is broken at the moment because virtqueue_add_inbuf()
>> fails due to both virtqueues (Rx and Tx) marked as broken by the
>> __vring_new_virtqueue() function. To solve this, virtio_device_ready()
>> (which unbreaks queues) should be called before virtqueue_add_inbuf().
>>
>> Fixes: 8b4ec69d7e09 ("virtio: harden vring IRQ")
>> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
>> ---
>>  drivers/rpmsg/virtio_rpmsg_bus.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
>> index 905ac7910c98..71a64d2c7644 100644
>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
>> @@ -929,6 +929,9 @@ static int rpmsg_probe(struct virtio_device *vdev)
>>  	/* and half is dedicated for TX */
>>  	vrp->sbufs = bufs_va + total_buf_space / 2;
>>  
>> +	/* From this point on, we can notify and get callbacks. */
>> +	virtio_device_ready(vdev);
>> +
> 
> Calling virtio_device_ready() here means that virtqueue_get_buf_ctx_split() can
> potentially be called (by way of rpmsg_recv_done()), which will race with
> virtqueue_add_inbuf().  If buffers in the virtqueue aren't available then
> rpmsg_recv_done() will fail, potentially breaking remote processors' state
> machines that don't expect their initial name service to fail when the "device"
> has been marked as ready.
> 
> What does make me curious though is that nobody on the remoteproc mailing list
> has complained about commit 8b4ec69d7e09 breaking their environment... By now,
> i.e rc4, that should have happened.  Anyone from TI, ST and Xilinx care to test this on
> their rig?

I tested on STm32mp1 board using tag v5.19-rc4(03c765b0e3b4)
I confirm the issue!

Concerning the solution, I share Mathieu's concern. This could break legacy.
I made a short test and I would suggest to use __virtio_unbreak_device instead, tounbreak the virtqueues without changing the init sequence.

I this case the patch would be: 
 
+	/*
+	 * Unbreak the virtqueues to allow to add buffers before setting the vdev status
+	 * to ready
+	 */
+	__virtio_unbreak_device(vdev);
+

 	/* set up the receive buffers */
 	for (i = 0; i < vrp->num_bufs / 2; i++) {
 		struct scatterlist sg;
 		void *cpu_addr = vrp->rbufs + i * vrp->buf_size;

Regards,
Arnaud
 
> 
> Thanks,
> Mathieu
> 
>>  	/* set up the receive buffers */
>>  	for (i = 0; i < vrp->num_bufs / 2; i++) {
>>  		struct scatterlist sg;
>> @@ -983,9 +986,6 @@ static int rpmsg_probe(struct virtio_device *vdev)
>>  	 */
>>  	notify = virtqueue_kick_prepare(vrp->rvq);
>>  
>> -	/* From this point on, we can notify and get callbacks. */
>> -	virtio_device_ready(vdev);
>> -
>>  	/* tell the remote processor it can start sending messages */
>>  	/*
>>  	 * this might be concurrent with callbacks, but we are only
>> -- 
>> 2.34.1
>>