Re: [PATCH v2 1/1] remoteproc: correct rproc_free_vring() to avoid invalid kernel paging

[Suman Anna]

Hi Loic,

On 07/26/2018 02:48 AM, Loic PALLARDY wrote:
> Hi Suman,
>>
>> Hi Loic,
>>
>> On 07/06/2018 02:46 AM, Loic Pallardy wrote:
>>> If rproc_start() failed, rproc_resource_cleanup() is called to clean
>>> debugfs entries, then associated iommu mappings, carveouts and vdev.
>>> Issue occurs when rproc_free_vring() is trying to reset vring resource
>>> table entry.
>>> At this time, table_ptr is pointing on loaded resource table and carveouts
>>> already released, so access to loaded resource table is generating a kernel
>>> paging error:
>>
>> Are you using a device specific CMA pool or carveout, and if so, where
>> the pool is? If not, where is the default CMA pool? I am trying to
>> reproduce the issue on my platform with the start failure as you
>> suggested, but haven't seen it so far. That said, I have seen the exact
>> same crash when using HighMEM CMA pools on my downstream kernel
>> when
>> stopping the processor, and the root cause is essentially the same as
>> what you summarized here. The issue was present with LowMem pools as
>> well, but got masked because of the kernel linear mapping.
> 
> I have a carveout declared in firmware resource table for co-processor code and data, and st driver has a specific 
> reserved memory region to fit fix address space requested by co-processor.
> So CPU access to code and loaded resource table area is granted thanks to allocation done by rproc_handle_carveout().

Where are the vrings getting allocated from?

In anycase, I prefer that we should actually reset the table_ptr in
rproc_start() in failure cases (undo the operation essentially) as we
don't call rproc_stop() in those cases. This will result in symmetric
code. We already have the reset handled in rproc_stop() added recently
in commit 0a8b81cb2e41 ("remoteproc: Reset table_ptr on stop"). Let me
know what you think, I can send a quick patch.

regards
Suman

> 
>>
>>>
>>> [   12.696535] Unable to handle kernel paging request at virtual address
>> f0f357cc
>>> [   12.696540] pgd = (ptrval)
>>> [   12.696542] [f0f357cc] *pgd=6d2d0811, *pte=00000000, *ppte=00000000
>>> [   12.696558] Internal error: Oops: 807 [#1] SMP ARM
>>> [   12.696563] Modules linked in: rpmsg_core v4l2_mem2mem
>> videobuf2_dma_contig sti_drm v4l2_common vida
>>> [   12.696598] CPU: 1 PID: 48 Comm: kworker/1:1 Tainted: G        W
>> 4.18.0-rc2-00018-g3170fdd-8
>>> [   12.696602] Hardware name: STi SoC with Flattened Device Tree
>>> [   12.696625] Workqueue: events request_firmware_work_func
>>> [   12.696659] PC is at rproc_free_vring+0x84/0xbc [remoteproc]
>>> [   12.696667] LR is at rproc_free_vring+0x70/0xbc [remoteproc]
>>>
>>> This patch proposes to simply remove reset of resource table vring entries,
>>> as firmware and resource table are reloaded at each rproc boot.
>>> rproc_trigger_recovery() not impacted as resources not touched during
>> recovery
>>> procedure.
>>
>> And error recovery doesn't work for me after the rproc_start, stop got
>> introduced.
> Recovery no available on B2260, but I'll test it on another platform this week
> 
> Regards,
> Loic
>>
>> regards
>> Suman
>>
>>>
>>> Signed-off-by: Loic Pallardy <loic.pallardy@xxxxxx>
>>> ---
>>> Changes from V1: typo fixes in commit message
>>>
>>>  drivers/remoteproc/remoteproc_core.c | 6 ------
>>>  1 file changed, 6 deletions(-)
>>>
>>> diff --git a/drivers/remoteproc/remoteproc_core.c
>> b/drivers/remoteproc/remoteproc_core.c
>>> index a9609d9..9a8b47c 100644
>>> --- a/drivers/remoteproc/remoteproc_core.c
>>> +++ b/drivers/remoteproc/remoteproc_core.c
>>> @@ -289,16 +289,10 @@ void rproc_free_vring(struct rproc_vring *rvring)
>>>  {
>>>  	int size = PAGE_ALIGN(vring_size(rvring->len, rvring->align));
>>>  	struct rproc *rproc = rvring->rvdev->rproc;
>>> -	int idx = rvring->rvdev->vring - rvring;
>>> -	struct fw_rsc_vdev *rsc;
>>>
>>>  	dma_free_coherent(rproc->dev.parent, size, rvring->va, rvring-
>>> dma);
>>>  	idr_remove(&rproc->notifyids, rvring->notifyid);
>>>
>>> -	/* reset resource entry info */
>>> -	rsc = (void *)rproc->table_ptr + rvring->rvdev->rsc_offset;
>>> -	rsc->vring[idx].da = 0;
>>> -	rsc->vring[idx].notifyid = -1;
>>>  }
>>>
>>>  static int rproc_vdev_do_probe(struct rproc_subdev *subdev)
>>>
>