linux-kernel - Re: [PATCH 06/10] swiotlb: use swiotlb_map_page in swiotlb_map_sg

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Message-ID: <9922f377-ee87-ba36-8d28-26af0f7822e5@arm.com>
Date:   Fri, 9 Nov 2018 16:37:54 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>,
        John Stultz <john.stultz@...aro.org>
Cc:     Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        konrad.wilk@...cle.com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH 06/10] swiotlb: use swiotlb_map_page in
 swiotlb_map_sg_attrs

On 09/11/2018 07:49, Christoph Hellwig wrote:
> On Tue, Nov 06, 2018 at 05:27:14PM -0800, John Stultz wrote:
>> But at that point if I just re-apply "swiotlb: use swiotlb_map_page in
>> swiotlb_map_sg_attrs", I reproduce the hangs.
>>
>> Any suggestions for how to further debug what might be going wrong
>> would be appreciated!
> 
> Very odd.  In the end map_sg and map_page are defined to do the same
> things to start with.  The only real issue we had in this area was:
> 
> "[PATCH v2] of/device: Really only set bus DMA mask when appropriate"
> 
> so with current mainline + that you still see a problem, and if you
> rever the commit we are replying to it still goes away?

OK, after quite a bit of trying I have managed to provoke a 
similar-looking problem with straight 4.20-rc1 on my Juno board - so far 
my "reproducer" is to decompress a ~10GB .tar.xz off an external USB 
hard disk, wherein after somewhere between 5 minutes and half an hour or 
so it tends to falls over with xz choking on corrupt data and/or a USB 
error.

 From the presentation, this really smells like there's some corner in 
which we're either missing cache maintenance or doing it to the wrong 
address - I've not seen any issues with Juno's main PCIe-attached I/O, 
but the EHCI here is non-coherent (and 32-bit, so the bus_dma_mask thing 
doesn't matter) as are the HiKey UFS and SD controller.

I'll keep digging...

Robin.