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Date:   Mon, 14 Jun 2021 17:33:39 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Tianyu Lan <ltykernel@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>, kys@microsoft.com,
        haiyangz@microsoft.com, sthemmin@microsoft.com, wei.liu@kernel.org,
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Subject: Re: [RFC PATCH V3 10/11] HV/Netvsc: Add Isolation VM support for
 netvsc driver
Message-ID: <20210614153339.GB1741@lst.de>
References: <20210530150628.2063957-1-ltykernel@gmail.com> <20210530150628.2063957-11-ltykernel@gmail.com> <20210607065007.GE24478@lst.de> <279cb4bf-c5b6-6db9-0f1e-9238e902c8f2@gmail.com> <20210614070903.GA29976@lst.de> <e10c2696-23c3-befe-4f4d-25e18918132f@gmail.com>
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On Mon, Jun 14, 2021 at 10:04:06PM +0800, Tianyu Lan wrote:
> The pages in the hv_page_buffer array here are in the kernel linear 
> mapping. The packet sent to host will contain an array which contains 
> transaction data. In the isolation VM, data in the these pages needs to be 
> copied to bounce buffer and so call dma_map_single() here to map these data 
> pages with bounce buffer. The vmbus has ring buffer where the send/receive 
> packets are copied to/from. The ring buffer has been remapped to the extra 
> space above shared gpa boundary/vTom during probing Netvsc driver and so 
> not call dma map function for vmbus ring
> buffer.

So why do we have all that PFN magic instead of using struct page or
the usual kernel I/O buffers that contain a page pointer?