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([2404:f801:9000:1a:efea::50b]) by smtp.gmail.com with ESMTPSA id h1sm3517800pfh.219.2021.12.06.06.19.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Dec 2021 06:19:32 -0800 (PST) Message-ID: <581569ce-b166-1cad-2624-66de319cc2b9@gmail.com> Date: Mon, 6 Dec 2021 22:19:21 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.3.2 Subject: Re: [PATCH V4 3/5] hyperv/IOMMU: Enable swiotlb bounce buffer for Isolation VM Content-Language: en-US To: Juergen Gross , 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, sstabellini@kernel.org, boris.ostrovsky@oracle.com, joro@8bytes.org, will@kernel.org, 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, xen-devel@lists.xenproject.org, 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, parri.andrea@gmail.com, dave.hansen@intel.com References: <20211205081815.129276-1-ltykernel@gmail.com> <20211205081815.129276-4-ltykernel@gmail.com> <125ffb7d-958c-e77a-243b-4cf38f690396@gmail.com> From: Tianyu Lan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/5/2021 6:31 PM, Juergen Gross wrote: > On 05.12.21 09:48, Tianyu Lan wrote: >> >> >> On 12/5/2021 4:34 PM, Juergen Gross wrote: >>> On 05.12.21 09:18, Tianyu Lan wrote: >>>> From: Tianyu Lan >>>> >>>> hyperv Isolation VM requires bounce buffer support to copy >>>> data from/to encrypted memory and so enable swiotlb force >>>> mode to use swiotlb bounce buffer for DMA transaction. >>>> >>>> In Isolation VM with AMD SEV, the 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. >>>> >>>> Hyper-V initalizes swiotlb bounce buffer and default swiotlb >>>> needs to be disabled. pci_swiotlb_detect_override() and >>>> pci_swiotlb_detect_4gb() enable the default one. To override >>>> the setting, hyperv_swiotlb_detect() needs to run before >>>> these detect functions which depends on the pci_xen_swiotlb_ >>>> init(). Make pci_xen_swiotlb_init() depends on the hyperv_swiotlb >>>> _detect() to keep the order. >>> >>> Why? Does Hyper-V plan to support Xen PV guests? If not, I don't see >>> the need for adding this change. >>> >> >> This is to keep detect function calling order that Hyper-V detect >> callback needs to call before pci_swiotlb_detect_override() and >> pci_swiotlb_detect_4gb(). This is the same for why >> pci_swiotlb_detect_override() needs to depend on the >> pci_xen_swiotlb_detect(). Hyper-V also has such request and so make >> xen detect callback depends on Hyper-V one. > > And does this even work without CONFIG_SWIOTLB_XEN, i.e. without > pci_xen_swiotlb_detect() being in the system? > Hi Juergen: Thanks for your review. This is a issue and I just sent out a v5 which decouples the dependency between xen and hyperv.