Documentation/virt/kvm: Document on Trust Domain Extensions (TDX)

yamahata · bonzini · commit 52f52ea79a4c · 2025-03-14T14:20:58.000-04:00
Add documentation to Intel Trusted Domain Extensions (TDX) support.

Signed-off-by: Isaku Yamahata &lt;isaku.yamahata@intel.com&gt;
Signed-off-by: Binbin Wu &lt;binbin.wu@linux.intel.com&gt;
Message-ID: &lt;20250227012021.1778144-21-binbin.wu@linux.intel.com&gt;
Signed-off-by: Paolo Bonzini &lt;pbonzini@redhat.com&gt;
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
@@ -1407,6 +1407,9 @@ the memory region are automatically reflected into the guest.  For example, an
 mmap() that affects the region will be made visible immediately.  Another
 example is madvise(MADV_DROP).
 
+For TDX guest, deleting/moving memory region loses guest memory contents.
+Read only region isn't supported.  Only as-id 0 is supported.
+
 Note: On arm64, a write generated by the page-table walker (to update
 the Access and Dirty flags, for example) never results in a
 KVM_EXIT_MMIO exit when the slot has the KVM_MEM_READONLY flag. This
@@ -4764,17 +4767,19 @@ H_GET_CPU_CHARACTERISTICS hypercall.
 
 :Capability: basic
 :Architectures: x86
-:Type: vm
+:Type: vm ioctl, vcpu ioctl
 :Parameters: an opaque platform specific structure (in/out)
 :Returns: 0 on success; -1 on error
 
 If the platform supports creating encrypted VMs then this ioctl can be used
 for issuing platform-specific memory encryption commands to manage those
 encrypted VMs.
 
-Currently, this ioctl is used for issuing Secure Encrypted Virtualization
-(SEV) commands on AMD Processors. The SEV commands are defined in
-Documentation/virt/kvm/x86/amd-memory-encryption.rst.
+Currently, this ioctl is used for issuing both Secure Encrypted Virtualization
+(SEV) commands on AMD Processors and Trusted Domain Extensions (TDX) commands
+on Intel Processors.  The detailed commands are defined in
+Documentation/virt/kvm/x86/amd-memory-encryption.rst and
+Documentation/virt/kvm/x86/intel-tdx.rst.
 
 4.111 KVM_MEMORY_ENCRYPT_REG_REGION
 -----------------------------------
diff --git a/Documentation/virt/kvm/x86/index.rst b/Documentation/virt/kvm/x86/index.rst
@@ -11,6 +11,7 @@ KVM for x86 systems
    cpuid
    errata
    hypercalls
+   intel-tdx
    mmu
    msr
    nested-vmx
diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst b/Documentation/virt/kvm/x86/intel-tdx.rst
@@ -0,0 +1,255 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+Intel Trust Domain Extensions (TDX)
+===================================
+
+Overview
+========
+Intel's Trust Domain Extensions (TDX) protect confidential guest VMs from the
+host and physical attacks.  A CPU-attested software module called 'the TDX
+module' runs inside a new CPU isolated range to provide the functionalities to
+manage and run protected VMs, a.k.a, TDX guests or TDs.
+
+Please refer to [1] for the whitepaper, specifications and other resources.
+
+This documentation describes TDX-specific KVM ABIs.  The TDX module needs to be
+initialized before it can be used by KVM to run any TDX guests.  The host
+core-kernel provides the support of initializing the TDX module, which is
+described in the Documentation/arch/x86/tdx.rst.
+
+API description
+===============
+
+KVM_MEMORY_ENCRYPT_OP
+---------------------
+:Type: vm ioctl, vcpu ioctl
+
+For TDX operations, KVM_MEMORY_ENCRYPT_OP is re-purposed to be generic
+ioctl with TDX specific sub-ioctl() commands.
+
+::
+
+  /* Trust Domain Extensions sub-ioctl() commands. */
+  enum kvm_tdx_cmd_id {
+          KVM_TDX_CAPABILITIES = 0,
+          KVM_TDX_INIT_VM,
+          KVM_TDX_INIT_VCPU,
+          KVM_TDX_INIT_MEM_REGION,
+          KVM_TDX_FINALIZE_VM,
+          KVM_TDX_GET_CPUID,
+
+          KVM_TDX_CMD_NR_MAX,
+  };
+
+  struct kvm_tdx_cmd {
+        /* enum kvm_tdx_cmd_id */
+        __u32 id;
+        /* flags for sub-command. If sub-command doesn't use this, set zero. */
+        __u32 flags;
+        /*
+         * data for each sub-command. An immediate or a pointer to the actual
+         * data in process virtual address.  If sub-command doesn't use it,
+         * set zero.
+         */
+        __u64 data;
+        /*
+         * Auxiliary error code.  The sub-command may return TDX SEAMCALL
+         * status code in addition to -Exxx.
+         */
+        __u64 hw_error;
+  };
+
+KVM_TDX_CAPABILITIES
+--------------------
+:Type: vm ioctl
+:Returns: 0 on success, <0 on error
+
+Return the TDX capabilities that current KVM supports with the specific TDX
+module loaded in the system.  It reports what features/capabilities are allowed
+to be configured to the TDX guest.
+
+- id: KVM_TDX_CAPABILITIES
+- flags: must be 0
+- data: pointer to struct kvm_tdx_capabilities
+- hw_error: must be 0
+
+::
+
+  struct kvm_tdx_capabilities {
+        __u64 supported_attrs;
+        __u64 supported_xfam;
+        __u64 reserved[254];
+
+        /* Configurable CPUID bits for userspace */
+        struct kvm_cpuid2 cpuid;
+  };
+
+
+KVM_TDX_INIT_VM
+---------------
+:Type: vm ioctl
+:Returns: 0 on success, <0 on error
+
+Perform TDX specific VM initialization.  This needs to be called after
+KVM_CREATE_VM and before creating any VCPUs.
+
+- id: KVM_TDX_INIT_VM
+- flags: must be 0
+- data: pointer to struct kvm_tdx_init_vm
+- hw_error: must be 0
+
+::
+
+  struct kvm_tdx_init_vm {
+          __u64 attributes;
+          __u64 xfam;
+          __u64 mrconfigid[6];          /* sha384 digest */
+          __u64 mrowner[6];             /* sha384 digest */
+          __u64 mrownerconfig[6];       /* sha384 digest */
+
+          /* The total space for TD_PARAMS before the CPUIDs is 256 bytes */
+          __u64 reserved[12];
+
+        /*
+         * Call KVM_TDX_INIT_VM before vcpu creation, thus before
+         * KVM_SET_CPUID2.
+         * This configuration supersedes KVM_SET_CPUID2s for VCPUs because the
+         * TDX module directly virtualizes those CPUIDs without VMM.  The user
+         * space VMM, e.g. qemu, should make KVM_SET_CPUID2 consistent with
+         * those values.  If it doesn't, KVM may have wrong idea of vCPUIDs of
+         * the guest, and KVM may wrongly emulate CPUIDs or MSRs that the TDX
+         * module doesn't virtualize.
+         */
+          struct kvm_cpuid2 cpuid;
+  };
+
+
+KVM_TDX_INIT_VCPU
+-----------------
+:Type: vcpu ioctl
+:Returns: 0 on success, <0 on error
+
+Perform TDX specific VCPU initialization.
+
+- id: KVM_TDX_INIT_VCPU
+- flags: must be 0
+- data: initial value of the guest TD VCPU RCX
+- hw_error: must be 0
+
+KVM_TDX_INIT_MEM_REGION
+-----------------------
+:Type: vcpu ioctl
+:Returns: 0 on success, <0 on error
+
+Initialize @nr_pages TDX guest private memory starting from @gpa with userspace
+provided data from @source_addr.
+
+Note, before calling this sub command, memory attribute of the range
+[gpa, gpa + nr_pages] needs to be private.  Userspace can use
+KVM_SET_MEMORY_ATTRIBUTES to set the attribute.
+
+If KVM_TDX_MEASURE_MEMORY_REGION flag is specified, it also extends measurement.
+
+- id: KVM_TDX_INIT_MEM_REGION
+- flags: currently only KVM_TDX_MEASURE_MEMORY_REGION is defined
+- data: pointer to struct kvm_tdx_init_mem_region
+- hw_error: must be 0
+
+::
+
+  #define KVM_TDX_MEASURE_MEMORY_REGION   (1UL << 0)
+
+  struct kvm_tdx_init_mem_region {
+          __u64 source_addr;
+          __u64 gpa;
+          __u64 nr_pages;
+  };
+
+
+KVM_TDX_FINALIZE_VM
+-------------------
+:Type: vm ioctl
+:Returns: 0 on success, <0 on error
+
+Complete measurement of the initial TD contents and mark it ready to run.
+
+- id: KVM_TDX_FINALIZE_VM
+- flags: must be 0
+- data: must be 0
+- hw_error: must be 0
+
+
+KVM_TDX_GET_CPUID
+-----------------
+:Type: vcpu ioctl
+:Returns: 0 on success, <0 on error
+
+Get the CPUID values that the TDX module virtualizes for the TD guest.
+When it returns -E2BIG, the user space should allocate a larger buffer and
+retry. The minimum buffer size is updated in the nent field of the
+struct kvm_cpuid2.
+
+- id: KVM_TDX_GET_CPUID
+- flags: must be 0
+- data: pointer to struct kvm_cpuid2 (in/out)
+- hw_error: must be 0 (out)
+
+::
+
+  struct kvm_cpuid2 {
+	  __u32 nent;
+	  __u32 padding;
+	  struct kvm_cpuid_entry2 entries[0];
+  };
+
+  struct kvm_cpuid_entry2 {
+	  __u32 function;
+	  __u32 index;
+	  __u32 flags;
+	  __u32 eax;
+	  __u32 ebx;
+	  __u32 ecx;
+	  __u32 edx;
+	  __u32 padding[3];
+  };
+
+KVM TDX creation flow
+=====================
+In addition to the standard KVM flow, new TDX ioctls need to be called.  The
+control flow is as follows:
+
+#. Check system wide capability
+
+   * KVM_CAP_VM_TYPES: Check if VM type is supported and if KVM_X86_TDX_VM
+     is supported.
+
+#. Create VM
+
+   * KVM_CREATE_VM
+   * KVM_TDX_CAPABILITIES: Query TDX capabilities for creating TDX guests.
+   * KVM_CHECK_EXTENSION(KVM_CAP_MAX_VCPUS): Query maximum VCPUs the TD can
+     support at VM level (TDX has its own limitation on this).
+   * KVM_SET_TSC_KHZ: Configure TD's TSC frequency if a different TSC frequency
+     than host is desired.  This is Optional.
+   * KVM_TDX_INIT_VM: Pass TDX specific VM parameters.
+
+#. Create VCPU
+
+   * KVM_CREATE_VCPU
+   * KVM_TDX_INIT_VCPU: Pass TDX specific VCPU parameters.
+   * KVM_SET_CPUID2: Configure TD's CPUIDs.
+   * KVM_SET_MSRS: Configure TD's MSRs.
+
+#. Initialize initial guest memory
+
+   * Prepare content of initial guest memory.
+   * KVM_TDX_INIT_MEM_REGION: Add initial guest memory.
+   * KVM_TDX_FINALIZE_VM: Finalize the measurement of the TDX guest.
+
+#. Run VCPU
+
+References
+==========
+
+.. [1] https://www.intel.com/content/www/us/en/developer/tools/trust-domain-extensions/documentation.html
