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Subject: Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address
 setting function
To:     Christoph Hellwig <hch@lst.de>, Tianyu Lan <ltykernel@gmail.com>
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References: <20210530150628.2063957-1-ltykernel@gmail.com>
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From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <94038087-a33c-93c5-27bf-7ec1f6f5f0e3@arm.com>
Date:   Mon, 14 Jun 2021 14:49:51 +0100
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On 2021-06-07 07:43, Christoph Hellwig wrote:
> On Sun, May 30, 2021 at 11:06:25AM -0400, Tianyu Lan wrote:
>> From: Tianyu Lan <Tianyu.Lan@microsoft.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?

FWIW, I think a better generalisation for this would be allowing 
set_memory_decrypted() to return an address rather than implicitly 
operating in-place, and hide all the various hypervisor hooks behind that.

Robin.