# Re: \[PATCH V7 1/5\] swiotlb: Add swiotlb bounce buffer remap function for HV IVM

- From: Tianyu Lan \<hidden\>
- Date: 2021-12-14 04:37:11 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/12/1607640
- Thread: https://ratatoskr.run/linux-arch/2021/12/1605563/t.md

```text
On 12/14/2021 12:45 AM, Dave Hansen wrote:
> On 12/12/21 11:14 PM, Tianyu Lan wrote:
>> In Isolation VM with AMD SEV, bounce buffer needs to be accessed via
>> extra address space which is above shared_gpa_boundary (E.G 39 bit
>> address line) reported by Hyper-V CPUID ISOLATION_CONFIG. The access
>> physical address will be original physical address + shared_gpa_boundary.
>> 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.
>
> This seems to be independently reintroducing some of the SEV
> infrastructure.  Is it really OK that this doesn't interact at all with
> any existing SEV code?
>
> For instance, do we need a new 'swiotlb_unencrypted_base', or should
> this just be using sme_me_mask somehow?

Hi Dave:
       Thanks for your review. Hyper-V provides a para-virtualized
confidential computing solution based on the AMD SEV function and not
expose sev&sme capabilities to guest. So sme_me_mask is unset in the
Hyper-V Isolation VM. swiotlb_unencrypted_base is more general solution
to handle such case of different address space for encrypted and
decrypted memory and other platform also may reuse it.
```