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Date:   Thu, 24 Jun 2021 12:18:56 +0100
From:   Will Deacon <will@kernel.org>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Claire Chang <tientzu@chromium.org>,
        Christoph Hellwig <hch@lst.de>,
        Qian Cai <quic_qiancai@quicinc.com>,
        Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
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Subject: Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing
Message-ID: <20210624111855.GA1382@willie-the-truck>
References: <20210619034043.199220-1-tientzu@chromium.org>
 <20210619034043.199220-7-tientzu@chromium.org>
 <76c3343d-72e5-9df3-8924-5474ee698ef4@quicinc.com>
 <20210623183736.GA472@willie-the-truck>
 <19d4c7a2-744d-21e0-289c-a576e1f0e6f3@quicinc.com>
 <20210624054315.GA25381@lst.de>
 <CALiNf288ZLMhY3E8E3N+z9rkwi1viWNLm1wwMEwT4rNwh3FfwQ@mail.gmail.com>
 <364e6715-eafd-fc4a-e0af-ce2a042756b4@arm.com>
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On Thu, Jun 24, 2021 at 12:14:39PM +0100, Robin Murphy wrote:
> On 2021-06-24 07:05, Claire Chang wrote:
> > On Thu, Jun 24, 2021 at 1:43 PM Christoph Hellwig <hch@lst.de> wrote:
> > > 
> > > On Wed, Jun 23, 2021 at 02:44:34PM -0400, Qian Cai wrote:
> > > > is_swiotlb_force_bounce at /usr/src/linux-next/./include/linux/swiotlb.h:119
> > > > 
> > > > is_swiotlb_force_bounce() was the new function introduced in this patch here.
> > > > 
> > > > +static inline bool is_swiotlb_force_bounce(struct device *dev)
> > > > +{
> > > > +     return dev->dma_io_tlb_mem->force_bounce;
> > > > +}
> > > 
> > > To me the crash looks like dev->dma_io_tlb_mem is NULL.  Can you
> > > turn this into :
> > > 
> > >          return dev->dma_io_tlb_mem && dev->dma_io_tlb_mem->force_bounce;
> > > 
> > > for a quick debug check?
> > 
> > I just realized that dma_io_tlb_mem might be NULL like Christoph
> > pointed out since swiotlb might not get initialized.
> > However,  `Unable to handle kernel paging request at virtual address
> > dfff80000000000e` looks more like the address is garbage rather than
> > NULL?
> > I wonder if that's because dev->dma_io_tlb_mem is not assigned
> > properly (which means device_initialize is not called?).
> 
> What also looks odd is that the base "address" 0xdfff800000000000 is held in
> a couple of registers, but the offset 0xe looks too small to match up to any
> relevant structure member in that dereference chain :/

FWIW, I've managed to trigger a NULL dereference locally when swiotlb hasn't
been initialised but we dereference 'dev->dma_io_tlb_mem', so I think
Christoph's suggestion is needed regardless. But I agree that it won't help
with the issue reported by Qian Cai.

Qian Cai: please can you share your .config and your command line?

Thanks,

Will