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Date:   Fri, 8 Jul 2022 10:00:52 +0200
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Subject: Re: [PATCH] rpmsg: virtio: Fix broken rpmsg_probe()
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To:     Jason Wang <jasowang@redhat.com>
CC:     "Michael S. Tsirkin" <mst@redhat.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Anup Patel <apatel@ventanamicro.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Atish Patra <atishp@atishpatra.org>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        Anup Patel <anup@brainfault.org>,
        <linux-remoteproc@vger.kernel.org>,
        <kvm-riscv@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        virtualization <virtualization@lists.linux-foundation.org>
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From:   Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>
In-Reply-To: <CACGkMEtOpG4LoNOVAfRkxziM-v09ZC=-Zn0O++8v_U66fNOp0g@mail.gmail.com>
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On 7/8/22 08:19, Jason Wang wrote:
> On Wed, Jul 6, 2022 at 2:57 PM Arnaud POULIQUEN
> <arnaud.pouliquen@foss.st.com> wrote:
>>
>>
>>
>> On 7/6/22 06:03, Jason Wang wrote:
>>> On Mon, Jul 4, 2022 at 5:45 PM Arnaud POULIQUEN
>>> <arnaud.pouliquen@foss.st.com> wrote:
>>>>
>>>> Hello Jason,
>>>>
>>>> On 7/4/22 06:35, Jason Wang wrote:
>>>>> On Fri, Jul 1, 2022 at 2:16 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>>>
>>>>>> On Fri, Jul 01, 2022 at 09:22:15AM +0800, Jason Wang wrote:
>>>>>>> On Fri, Jul 1, 2022 at 3:20 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>>>>>
>>>>>>>> On Thu, Jun 30, 2022 at 11:51:30AM -0600, Mathieu Poirier wrote:
>>>>>>>>> + virtualization@lists.linux-foundation.org
>>>>>>>>> + jasowang@redhat.com
>>>>>>>>> + mst@redhat.com
>>>>>>>>>
>>>>>>>>> On Thu, 30 Jun 2022 at 10:20, Arnaud POULIQUEN
>>>>>>>>> <arnaud.pouliquen@foss.st.com> wrote:
>>>>>>>>>>
>>>>>>>>>> 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@ventanamicro.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;
>>>>>>>>>
>>>>>>>>> This will indeed fix the problem.  On the flip side the kernel
>>>>>>>>> documentation for __virtio_unbreak_device() puzzles me...
>>>>>>>>> It clearly states that it should be used for probing and restoring but
>>>>>>>>> _not_ directly by the driver.  Function rpmsg_probe() is part of
>>>>>>>>> probing but also the entry point to a driver.
>>>>>>>>>
>>>>>>>>> Michael and virtualisation folks, is this the right way to move forward?
>>>>>>>>
>>>>>>>> I don't think it is, __virtio_unbreak_device is intended for core use.
>>>>>>>
>>>>>>> Can we fill the rx after virtio_device_ready() in this case?
>>>>>>>
>>>>>>> Btw, the driver set driver ok after registering, we probably get a svq
>>>>>>> kick before DRIVER_OK?
>>>>
>>>> By "registering" you mean calling rpmsg_virtio_add_ctrl_dev and
>>>> rpmsg_ns_register_device?
>>>
>>> Yes.
>>>
>>>>
>>>> The rpmsg_ns_register_device has to be called before. Because it has to be
>>>> probed to handle the first message coming from the remote side to create
>>>> associated rpmsg local device.
>>>
>>> I couldn't find the code to do this, maybe you can give me some hint on this.
>>
>> The rpmsg_ns is available here :
>> https://elixir.bootlin.com/linux/latest/source/drivers/rpmsg/rpmsg_ns.c
>>
>> It is probed on rpmsg_ns_register_device call.
>> https://elixir.bootlin.com/linux/latest/source/drivers/rpmsg/virtio_rpmsg_bus.c#L974
> 
> Yes but what I want to ask is, it looks to me
> rpmsg_ns_register_device() only creates a rpmsg device. Do you mean
> the rpmsg driver that will handle the first message during its probe?

No it will be out of its probe, in its callback. the callback is called
by the virtio-rpmsg based on the rpmsg receiver address.

For the details:
In rpmsg virtio implementation there is a mechanism to discover the
RPMsg services supported by the remote processor: the name service
announcement. For instance for the rpmsg_tty[1], the remote processor
sends a rpmsg service announcement message indicating that it supports
the "rpmsg-tty" service.
On linux side the rpmsg_ns receives the message and creates a rpmsg
channel that leads to a rpmsg_tty device creation on the rpmsg bus.

If the rpmsg_ns is not registered (so no rpmsg receiver address
registered), then when the "ns announcement" is received,the message
is dropped, the service not initialized.

[1]:https://elixir.bootlin.com/linux/v5.19-rc4/source/drivers/tty/rpmsg_tty.c

> 
>>
>>
>>>
>>>> It doesn't send message.
>>>
>>> I see the function register the device to the bus, I wonder if this
>>> means the device could be probed and used by the driver before
>>> virtio_device_ready().
>>>
>>>>
>>>> The risk could be for the rpmsg_ctrl device. Registering it
>>>> after the virtio_device_ready(vdev) call could make sense...
>>>
>>> I see.
>>>
>>>>
>>>>>>>
>>>>>>> Thanks
>>>>>>
>>>>>> Is this an ack for the original patch?
>>>>>
>>>>> Nope, I meant, instead of moving virtio_device_ready() a little bit
>>>>> earlier, can we only move the rvq filling after virtio_device_ready().
>>>>>
>>>>> Thanks
>>>>
>>>> Please find some concerns about this inversion here:
>>>> https://lore.kernel.org/lkml/20220701053813-mutt-send-email-mst@kernel.org/
>>>>
>>>> Regarding __virtio_unbreak_device. The pending virtio_break_device is
>>>> used by some virtio driver.
>>>> Could we consider that it makes sense to also have a
>>>> virtio_unbreak_device interface?
>>>
>>> We don't want to allow the driver to unbreak a device since it's
>>> easier to have bugs.
>>>
>>>>
>>>>
>>>> I do not well understand the reason of the commit:
>>>> 8b4ec69d7e09 ("virtio: harden vring IRQ", 2022-05-27)
>>>
>>> It tries to forbid the virtqueue callbacks to be called before
>>> virtio_device_ready(). This helps to prevent the malicious device from
>>> attacking the driver.
>>>
>>> But unfortunately, it breaks several driver because:
>>>
>>> 1) some driver have races in probe/remove
>>> 2) it tries to reuse vq->broken which may break the driver that call
>>> virqueue_add() before virtio_device_ready() which is allowed by the
>>> spec
>>>
>>> There's a discussion to have a better behavior that doesn't break the
>>> existing drivers. And the IRQ hardening feature is marked as broken
>>> now, so rpmsg should be fine without any extra effort.
>>
>> Thanks for the explanations.
>> If the discussions are in a mail thread could you give me the reference?
> 
> Here're the discussions and commits:
> 
> https://lore.kernel.org/lkml/20220622012940.21441-1-jasowang@redhat.com/
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/commit/?h=linux-next&id=c346dae4f3fbce51bbd4f2ec5e8c6f9b91e93163
> https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/commit/?h=linux-next&id=6a9720576cd00d30722c5f755bd17d4cfa9df636

Thanks for the links!
So no more update planed in drivers/rpmsg/virtio_rpmsg_bus.c, if i well understood...
 
Thanks,
Arnaud

> 
> Thanks
> 
>>
>> Thanks,
>> Arnaud
>>
>>>
>>>> So following alternative is probably pretty naive:
>>>> Is the use of virtqueue_disable_cb could be an alternative to the
>>>> vq->broken usage allowing to register buffer while preventing virtqueue IRQ?
>>>
>>> Probably not, there's no guarantee that the device will not send
>>> notification after virqtueue_disable_cb().
>>>
>>> Thanks
>>>
>>>>
>>>> Thanks,
>>>> Arnaud
>>>>
>>>>>
>>>>>>
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 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
>>>>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>