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@xxxxxxxxxxxxx> 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? Juergen
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