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

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Date:   Mon, 14 Jun 2021 21:42:00 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
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Subject: Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address
 setting function

On 6/14/2021 9:37 PM, Tianyu Lan wrote:
> 
> 
> On 6/14/2021 3:12 PM, Christoph Hellwig wrote:
>> On Mon, Jun 07, 2021 at 10:56:47PM +0800, Tianyu Lan wrote:
>>> These addresses in extra address space works as system memory mirror. 
>>> The
>>> shared memory with host in Isolation VM needs to be accessed via extra
>>> address space which is above shared gpa boundary.
>>
>> Why?
>>
> 
> The shared_gpa_boundary in the AMD SEV SNP spec is called virtual top of
> memory(vTOM). Memory addresses below vTOM are automatically treated as
> private while memory above vTOM is treated as shared. Using vTOM to
> separate memory in this way avoids the need to augment the standard x86
> page tables with C-bit markings, simplifying guest OS software.

Here is the spec link and vTOM description is in the page 14.
https://www.amd.com/system/files/TechDocs/SEV-SNP-strengthening-vm-isolation-with-integrity-protection-and-more.pdf

Thanks.