Message-ID: <3243ff22-f6c8-b7cd-26b7-6e917e274a7c@gmail.com>
Date:   Tue, 14 Dec 2021 12:36:56 +0800
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From:   Tianyu Lan <ltykernel@gmail.com>
Subject: Re: [PATCH V7 1/5] swiotlb: Add swiotlb bounce buffer remap function
 for HV IVM
To:     Dave Hansen <dave.hansen@intel.com>, kys@microsoft.com,
        haiyangz@microsoft.com, sthemmin@microsoft.com, wei.liu@kernel.org,
        decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
        hpa@zytor.com, davem@davemloft.net, kuba@kernel.org,
        jejb@linux.ibm.com, martin.petersen@oracle.com, arnd@arndb.de,
        hch@infradead.org, m.szyprowski@samsung.com, robin.murphy@arm.com,
        thomas.lendacky@amd.com, Tianyu.Lan@microsoft.com,
        michael.h.kelley@microsoft.com
Cc:     iommu@lists.linux-foundation.org, linux-arch@vger.kernel.org,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-scsi@vger.kernel.org, netdev@vger.kernel.org,
        vkuznets@redhat.com, brijesh.singh@amd.com, konrad.wilk@oracle.com,
        hch@lst.de, joro@8bytes.org, parri.andrea@gmail.com
References: <20211213071407.314309-1-ltykernel@gmail.com>
 <20211213071407.314309-2-ltykernel@gmail.com>
 <198e9243-abca-b23e-0e8e-8581a7329ede@intel.com>
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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.