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

[Loic PALLARDY <loic.pallardy@st.com>]

Hi Suman, 

> -----Original Message-----
> From: Suman Anna <s-anna@ti.com>
> Sent: Friday, July 27, 2018 1:52 AM
> To: Loic PALLARDY <loic.pallardy@st.com>; bjorn.andersson@linaro.org;
> ohad@wizery.com
> Cc: linux-remoteproc@vger.kernel.org; linux-kernel@vger.kernel.org;
> Arnaud POULIQUEN <arnaud.pouliquen@st.com>;
> benjamin.gaignard@linaro.org
> Subject: Re: [PATCH v2 1/1] remoteproc: correct rproc_free_vring() to avoid
> invalid kernel paging
> 
> 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?

Vrings are allocated from same reserved memory region assigned to ST platform driver.
> 
> 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.

Agree better to have symmetric code. Should be OK. I'll tested .

Regards,
Loic
> 
> 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@st.com>
> >>> ---
> >>> 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)
> >>>
> >