linux-kernel - Re: [PATCH V7 1/5] swiotlb: Add swiotlb bounce buffer remap function for HV IVM

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Date:   Tue, 14 Dec 2021 10:40:49 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tianyu Lan <ltykernel@...il.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, davem@...emloft.net, kuba@...nel.org,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, arnd@...db.de,
        hch@...radead.org, m.szyprowski@...sung.com, robin.murphy@....com,
        thomas.lendacky@....com, Tianyu.Lan@...rosoft.com,
        michael.h.kelley@...rosoft.com
Cc:     iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, netdev@...r.kernel.org,
        vkuznets@...hat.com, brijesh.singh@....com, konrad.wilk@...cle.com,
        hch@....de, joro@...tes.org, parri.andrea@...il.com
Subject: Re: [PATCH V7 1/5] swiotlb: Add swiotlb bounce buffer remap function
 for HV IVM

On 12/13/21 8:36 PM, Tianyu Lan wrote:
> 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?
> 
>        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.

I don't really understand how this can be more general any *not* get
utilized by the existing SEV support.