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Date:   Wed, 23 Jun 2021 19:37:37 +0100
From:   Will Deacon <will@kernel.org>
To:     Qian Cai <quic_qiancai@quicinc.com>
Cc:     Claire Chang <tientzu@chromium.org>,
        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: <20210623183736.GA472@willie-the-truck>
References: <20210619034043.199220-1-tientzu@chromium.org>
 <20210619034043.199220-7-tientzu@chromium.org>
 <76c3343d-72e5-9df3-8924-5474ee698ef4@quicinc.com>
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On Wed, Jun 23, 2021 at 12:39:29PM -0400, Qian Cai wrote:
> 
> 
> On 6/18/2021 11:40 PM, Claire Chang wrote:
> > Propagate the swiotlb_force into io_tlb_default_mem->force_bounce and
> > use it to determine whether to bounce the data or not. This will be
> > useful later to allow for different pools.
> > 
> > Signed-off-by: Claire Chang <tientzu@chromium.org>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Tested-by: Stefano Stabellini <sstabellini@kernel.org>
> > Tested-by: Will Deacon <will@kernel.org>
> > Acked-by: Stefano Stabellini <sstabellini@kernel.org>
> 
> Reverting the rest of the series up to this patch fixed a boot crash with NVMe on today's linux-next.

Hmm, so that makes patch 7 the suspicious one, right?

Looking at that one more closely, it looks like swiotlb_find_slots() takes
'alloc_size + offset' as its 'alloc_size' parameter from
swiotlb_tbl_map_single() and initialises 'mem->slots[i].alloc_size' based
on 'alloc_size + offset', which looks like a change in behaviour from the
old code, which didn't include the offset there.

swiotlb_release_slots() then adds the offset back on afaict, so we end up
accounting for it twice and possibly unmap more than we're supposed to?

Will