269 lines
7.3 KiB
ReStructuredText
269 lines
7.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===================================
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Intel Trust Domain Extensions (TDX)
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===================================
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Overview
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========
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Intel's Trust Domain Extensions (TDX) protect confidential guest VMs from the
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host and physical attacks. A CPU-attested software module called 'the TDX
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module' runs inside a new CPU isolated range to provide the functionalities to
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manage and run protected VMs, a.k.a, TDX guests or TDs.
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Please refer to [1] for the whitepaper, specifications and other resources.
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This documentation describes TDX-specific KVM ABIs. The TDX module needs to be
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initialized before it can be used by KVM to run any TDX guests. The host
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core-kernel provides the support of initializing the TDX module, which is
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described in the Documentation/arch/x86/tdx.rst.
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API description
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===============
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KVM_MEMORY_ENCRYPT_OP
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---------------------
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:Type: vm ioctl, vcpu ioctl
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For TDX operations, KVM_MEMORY_ENCRYPT_OP is re-purposed to be generic
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ioctl with TDX specific sub-ioctl() commands.
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::
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/* Trust Domain Extensions sub-ioctl() commands. */
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enum kvm_tdx_cmd_id {
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KVM_TDX_CAPABILITIES = 0,
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KVM_TDX_INIT_VM,
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KVM_TDX_INIT_VCPU,
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KVM_TDX_INIT_MEM_REGION,
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KVM_TDX_FINALIZE_VM,
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KVM_TDX_GET_CPUID,
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KVM_TDX_CMD_NR_MAX,
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};
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struct kvm_tdx_cmd {
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/* enum kvm_tdx_cmd_id */
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__u32 id;
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/* flags for sub-command. If sub-command doesn't use this, set zero. */
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__u32 flags;
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/*
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* data for each sub-command. An immediate or a pointer to the actual
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* data in process virtual address. If sub-command doesn't use it,
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* set zero.
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*/
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__u64 data;
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/*
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* Auxiliary error code. The sub-command may return TDX SEAMCALL
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* status code in addition to -Exxx.
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*/
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__u64 hw_error;
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};
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KVM_TDX_CAPABILITIES
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--------------------
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:Type: vm ioctl
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:Returns: 0 on success, <0 on error
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Return the TDX capabilities that current KVM supports with the specific TDX
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module loaded in the system. It reports what features/capabilities are allowed
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to be configured to the TDX guest.
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- id: KVM_TDX_CAPABILITIES
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- flags: must be 0
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- data: pointer to struct kvm_tdx_capabilities
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- hw_error: must be 0
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::
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struct kvm_tdx_capabilities {
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__u64 supported_attrs;
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__u64 supported_xfam;
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/* TDG.VP.VMCALL hypercalls executed in kernel and forwarded to
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* userspace, respectively
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*/
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__u64 kernel_tdvmcallinfo_1_r11;
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__u64 user_tdvmcallinfo_1_r11;
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/* TDG.VP.VMCALL instruction executions subfunctions executed in kernel
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* and forwarded to userspace, respectively
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*/
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__u64 kernel_tdvmcallinfo_1_r12;
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__u64 user_tdvmcallinfo_1_r12;
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__u64 reserved[250];
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/* Configurable CPUID bits for userspace */
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struct kvm_cpuid2 cpuid;
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};
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KVM_TDX_INIT_VM
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---------------
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:Type: vm ioctl
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:Returns: 0 on success, <0 on error
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Perform TDX specific VM initialization. This needs to be called after
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KVM_CREATE_VM and before creating any VCPUs.
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- id: KVM_TDX_INIT_VM
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- flags: must be 0
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- data: pointer to struct kvm_tdx_init_vm
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- hw_error: must be 0
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::
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struct kvm_tdx_init_vm {
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__u64 attributes;
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__u64 xfam;
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__u64 mrconfigid[6]; /* sha384 digest */
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__u64 mrowner[6]; /* sha384 digest */
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__u64 mrownerconfig[6]; /* sha384 digest */
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/* The total space for TD_PARAMS before the CPUIDs is 256 bytes */
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__u64 reserved[12];
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/*
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* Call KVM_TDX_INIT_VM before vcpu creation, thus before
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* KVM_SET_CPUID2.
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* This configuration supersedes KVM_SET_CPUID2s for VCPUs because the
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* TDX module directly virtualizes those CPUIDs without VMM. The user
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* space VMM, e.g. qemu, should make KVM_SET_CPUID2 consistent with
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* those values. If it doesn't, KVM may have wrong idea of vCPUIDs of
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* the guest, and KVM may wrongly emulate CPUIDs or MSRs that the TDX
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* module doesn't virtualize.
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*/
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struct kvm_cpuid2 cpuid;
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};
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KVM_TDX_INIT_VCPU
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-----------------
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:Type: vcpu ioctl
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:Returns: 0 on success, <0 on error
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Perform TDX specific VCPU initialization.
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- id: KVM_TDX_INIT_VCPU
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- flags: must be 0
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- data: initial value of the guest TD VCPU RCX
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- hw_error: must be 0
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KVM_TDX_INIT_MEM_REGION
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-----------------------
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:Type: vcpu ioctl
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:Returns: 0 on success, <0 on error
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Initialize @nr_pages TDX guest private memory starting from @gpa with userspace
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provided data from @source_addr.
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Note, before calling this sub command, memory attribute of the range
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[gpa, gpa + nr_pages] needs to be private. Userspace can use
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KVM_SET_MEMORY_ATTRIBUTES to set the attribute.
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If KVM_TDX_MEASURE_MEMORY_REGION flag is specified, it also extends measurement.
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- id: KVM_TDX_INIT_MEM_REGION
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- flags: currently only KVM_TDX_MEASURE_MEMORY_REGION is defined
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- data: pointer to struct kvm_tdx_init_mem_region
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- hw_error: must be 0
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::
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#define KVM_TDX_MEASURE_MEMORY_REGION (1UL << 0)
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struct kvm_tdx_init_mem_region {
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__u64 source_addr;
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__u64 gpa;
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__u64 nr_pages;
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};
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KVM_TDX_FINALIZE_VM
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-------------------
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:Type: vm ioctl
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:Returns: 0 on success, <0 on error
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Complete measurement of the initial TD contents and mark it ready to run.
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- id: KVM_TDX_FINALIZE_VM
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- flags: must be 0
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- data: must be 0
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- hw_error: must be 0
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KVM_TDX_GET_CPUID
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-----------------
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:Type: vcpu ioctl
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:Returns: 0 on success, <0 on error
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Get the CPUID values that the TDX module virtualizes for the TD guest.
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When it returns -E2BIG, the user space should allocate a larger buffer and
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retry. The minimum buffer size is updated in the nent field of the
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struct kvm_cpuid2.
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- id: KVM_TDX_GET_CPUID
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- flags: must be 0
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- data: pointer to struct kvm_cpuid2 (in/out)
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- hw_error: must be 0 (out)
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::
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struct kvm_cpuid2 {
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__u32 nent;
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__u32 padding;
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struct kvm_cpuid_entry2 entries[0];
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};
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struct kvm_cpuid_entry2 {
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__u32 function;
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__u32 index;
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__u32 flags;
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__u32 eax;
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__u32 ebx;
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__u32 ecx;
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__u32 edx;
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__u32 padding[3];
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};
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KVM TDX creation flow
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=====================
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In addition to the standard KVM flow, new TDX ioctls need to be called. The
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control flow is as follows:
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#. Check system wide capability
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* KVM_CAP_VM_TYPES: Check if VM type is supported and if KVM_X86_TDX_VM
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is supported.
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#. Create VM
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* KVM_CREATE_VM
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* KVM_TDX_CAPABILITIES: Query TDX capabilities for creating TDX guests.
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* KVM_CHECK_EXTENSION(KVM_CAP_MAX_VCPUS): Query maximum VCPUs the TD can
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support at VM level (TDX has its own limitation on this).
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* KVM_SET_TSC_KHZ: Configure TD's TSC frequency if a different TSC frequency
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than host is desired. This is Optional.
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* KVM_TDX_INIT_VM: Pass TDX specific VM parameters.
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#. Create VCPU
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* KVM_CREATE_VCPU
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* KVM_TDX_INIT_VCPU: Pass TDX specific VCPU parameters.
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* KVM_SET_CPUID2: Configure TD's CPUIDs.
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* KVM_SET_MSRS: Configure TD's MSRs.
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#. Initialize initial guest memory
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* Prepare content of initial guest memory.
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* KVM_TDX_INIT_MEM_REGION: Add initial guest memory.
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* KVM_TDX_FINALIZE_VM: Finalize the measurement of the TDX guest.
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#. Run VCPU
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References
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==========
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.. [1] https://www.intel.com/content/www/us/en/developer/tools/trust-domain-extensions/documentation.html
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