linux-kernel - Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address setting function

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Message-ID: <20210607064312.GB24478@lst.de>
Date:   Mon, 7 Jun 2021 08:43:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
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        hannes@...xchg.org, cai@....pw, krish.sadhukhan@...cle.com,
        saravanand@...com, Tianyu.Lan@...rosoft.com,
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Subject: Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address
 setting function

On Sun, May 30, 2021 at 11:06:25AM -0400, Tianyu Lan wrote:
> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> 
> For Hyper-V isolation VM with AMD SEV SNP, the bounce buffer(shared memory)
> needs to be accessed via extra address space(e.g address above bit39).
> Hyper-V code may remap extra address space outside of swiotlb. swiotlb_
> bounce() needs to use remap virtual address to copy data from/to bounce
> buffer. Add new interface swiotlb_set_bounce_remap() to do that.

Why can't you use the bus_dma_region ranges to remap to your preferred
address?