Messages in this thread | | | Date | Mon, 6 Dec 2021 22:19:21 +0800 | Subject | Re: [PATCH V4 3/5] hyperv/IOMMU: Enable swiotlb bounce buffer for Isolation VM | From | Tianyu Lan <> |
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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 <Tianyu.Lan@microsoft.com> >>>> >>>> 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.
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