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.
