Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address
 setting function
From:   Tianyu Lan <ltykernel@gmail.com>
To:     Christoph Hellwig <hch@lst.de>
Cc:     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, x86@kernel.org, hpa@zytor.com,
        arnd@arndb.de, dave.hansen@linux.intel.com, luto@kernel.org,
        peterz@infradead.org, akpm@linux-foundation.org,
        kirill.shutemov@linux.intel.com, rppt@kernel.org,
        hannes@cmpxchg.org, cai@lca.pw, krish.sadhukhan@oracle.com,
        saravanand@fb.com, Tianyu.Lan@microsoft.com,
        konrad.wilk@oracle.com, m.szyprowski@samsung.com,
        robin.murphy@arm.com, boris.ostrovsky@oracle.com, jgross@suse.com,
        sstabellini@kernel.org, joro@8bytes.org, will@kernel.org,
        xen-devel@lists.xenproject.org, davem@davemloft.net,
        kuba@kernel.org, jejb@linux.ibm.com, martin.petersen@oracle.com,
        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, thomas.lendacky@amd.com,
        brijesh.singh@amd.com, sunilmut@microsoft.com
References: <20210530150628.2063957-1-ltykernel@gmail.com>
 <20210530150628.2063957-9-ltykernel@gmail.com>
 <20210607064312.GB24478@lst.de>
 <48516ce3-564c-419e-b355-0ce53794dcb1@gmail.com>
 <20210614071223.GA30171@lst.de>
 <3e64e59b-7440-69a5-75c5-43225f3d6c0a@gmail.com>
Message-ID: <ee3d79ea-f4f9-b886-e1ee-e26b42a88530@gmail.com>
Date:   Mon, 14 Jun 2021 21:42:00 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <3e64e59b-7440-69a5-75c5-43225f3d6c0a@gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.