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

[Suman Anna]

On 07/26/2018 06:51 PM, Suman Anna wrote:
> 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.

FYI, patch for the same posted here,
https://patchwork.kernel.org/patch/10546555/

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)
>>>>
>>
>