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Date:   Wed, 16 Nov 2022 00:15:06 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Jonathan Lemon <jonathan.lemon@gmail.com>
Cc:     io-uring@vger.kernel.org, kernel-team@meta.com
Subject: Re: [PATCH v1 07/15] io_uring: Allocate zctap device buffers and dma
 map them.
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> +		dma_unmap_page_attrs(device, buf->dma, PAGE_SIZE,
> +				     DMA_BIDIRECTIONAL,
> +				     DMA_ATTR_SKIP_CPU_SYNC);

> +		addr = dma_map_page_attrs(device, page, 0, PAGE_SIZE,
> +					  DMA_BIDIRECTIONAL,
> +					  DMA_ATTR_SKIP_CPU_SYNC);

You can't just magically skip cpu syncs.  The flag is only valid
for mappings of already mapped memory when following a very careful
protocol.  I can't see any indications of that beeing true here,
but maybe I'm just missing something.