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Subject: Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing
To:     Will Deacon <will@kernel.org>
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,
        Joerg Roedel <joro@8bytes.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        boris.ostrovsky@oracle.com, jgross@suse.com,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        heikki.krogerus@linux.intel.com, thomas.hellstrom@linux.intel.com,
        peterz@infradead.org, benh@kernel.crashing.org,
        joonas.lahtinen@linux.intel.com, dri-devel@lists.freedesktop.org,
        chris@chris-wilson.co.uk, grant.likely@arm.com, paulus@samba.org,
        mingo@kernel.org, Jianxiong Gao <jxgao@google.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Saravana Kannan <saravanak@google.com>, xypron.glpk@gmx.de,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        bskeggs@redhat.com, linux-pci@vger.kernel.org,
        xen-devel@lists.xenproject.org,
        Thierry Reding <treding@nvidia.com>,
        intel-gfx@lists.freedesktop.org, matthew.auld@intel.com,
        linux-devicetree <devicetree@vger.kernel.org>,
        Daniel Vetter <daniel@ffwll.ch>, airlied@linux.ie,
        maarten.lankhorst@linux.intel.com, linuxppc-dev@lists.ozlabs.org,
        jani.nikula@linux.intel.com,
        Nicolas Boichat <drinkcat@chromium.org>,
        rodrigo.vivi@intel.com, Bjorn Helgaas <bhelgaas@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
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        Jim Quinlan <james.quinlan@broadcom.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, bauerman@linux.ibm.com
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>
 <20210624111855.GA1382@willie-the-truck>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <452155d2-c98e-23f6-86d6-3a2ff2e74783@arm.com>
Date:   Thu, 24 Jun 2021 12:34:09 +0100
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On 2021-06-24 12:18, Will Deacon wrote:
> 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.

Ack to that - for SWIOTLB_NO_FORCE, io_tlb_default_mem will remain NULL. 
The massive jump in KernelCI baseline failures as of yesterday looks 
like every arm64 machine with less than 4GB of RAM blowing up...

Robin.

> 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
>