[RFC PATCH v6 102/104] Documentation/virtual/kvm: Document on Trust Domain Extensions(TDX)

[isaku.yamahata@intel.com]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Add documentation to Intel Trusted Domain Extensions(TDX) support.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 Documentation/virt/kvm/api.rst       |   9 +-
 Documentation/virt/kvm/intel-tdx.rst | 381 +++++++++++++++++++++++++++
 2 files changed, 389 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/virt/kvm/intel-tdx.rst

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 7fa6850f1e81..09691d3a6b4a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1394,6 +1394,9 @@ It is recommended to use this API instead of the KVM_SET_MEMORY_REGION ioctl.
 The KVM_SET_MEMORY_REGION does not allow fine grained control over memory
 allocation and is deprecated.
 
+For TDX guest, deleting/moving memory region loses guest memory contents.
+Read only region isn't supported.  Only as-id 0 is supported.
+
 
 4.36 KVM_SET_TSS_ADDR
 ---------------------
@@ -4625,7 +4628,7 @@ 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
 
@@ -4637,6 +4640,10 @@ Currently, this ioctl is used for issuing Secure Encrypted Virtualization
 (SEV) commands on AMD Processors. The SEV commands are defined in
 Documentation/virt/kvm/amd-memory-encryption.rst.
 
+Currently, this ioctl is used for issuing Trusted Domain Extensions
+(TDX) commands on Intel Processors. The TDX commands are defined in
+Documentation/virt/kvm/intel-tdx.rst.
+
 4.111 KVM_MEMORY_ENCRYPT_REG_REGION
 -----------------------------------
 
diff --git a/Documentation/virt/kvm/intel-tdx.rst b/Documentation/virt/kvm/intel-tdx.rst
new file mode 100644
index 000000000000..3fae2cf9e534
--- /dev/null
+++ b/Documentation/virt/kvm/intel-tdx.rst
@@ -0,0 +1,381 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+Intel Trust Dodmain Extensions(TDX)
+===================================
+
+Overview
+========
+TDX stands for Trust Domain Extensions which isolates VMs from
+the virtual-machine manager (VMM)/hypervisor and any other software on
+the platform. [1]
+For details, the specifications, [2], [3], [4], [5], [6], [7], are
+available.
+
+
+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 command.
+
+::
+
+  /* Trust Domain eXtension 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_CMD_NR_MAX,
+  };
+
+  struct kvm_tdx_cmd {
+        /* enum kvm_tdx_cmd_id */
+        __u32 id;
+        /* flags for sub-commend. 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.
+         * Defined for consistency with struct kvm_sev_cmd.
+         */
+        __u64 error;
+        /* Reserved: Defined for consistency with struct kvm_sev_cmd. */
+        __u64 unused;
+  };
+
+KVM_TDX_CAPABILITIES
+--------------------
+:Type: vm ioctl
+
+Subset of TDSYSINFO_STRCUCT retrieved by TDH.SYS.INFO TDX SEAM call will be
+returned. Which describes about Intel TDX module.
+
+- id: KVM_TDX_CAPABILITIES
+- flags: must be 0
+- data: pointer to struct kvm_tdx_capabilities
+- error: must be 0
+- unused: must be 0
+
+::
+
+  struct kvm_tdx_cpuid_config {
+          __u32 leaf;
+          __u32 sub_leaf;
+          __u32 eax;
+          __u32 ebx;
+          __u32 ecx;
+          __u32 edx;
+  };
+
+  struct kvm_tdx_capabilities {
+          __u64 attrs_fixed0;
+          __u64 attrs_fixed1;
+          __u64 xfam_fixed0;
+          __u64 xfam_fixed1;
+
+          __u32 nr_cpuid_configs;
+          struct kvm_tdx_cpuid_config cpuid_configs[0];
+  };
+
+
+KVM_TDX_INIT_VM
+---------------
+:Type: vm ioctl
+
+Does additional VM initialization specific to TDX which corresponds to
+TDH.MNG.INIT TDX SEAM call.
+
+- id: KVM_TDX_INIT_VM
+- flags: must be 0
+- data: pointer to struct kvm_tdx_init_vm
+- error: must be 0
+- unused: must be 0
+
+::
+
+  struct kvm_tdx_init_vm {
+          __u32 max_vcpus;
+          __u32 reserved;
+          __u64 attributes;
+          __u64 cpuid;  /* pointer to struct kvm_cpuid2 */
+          __u64 mrconfigid[6];          /* sha384 digest */
+          __u64 mrowner[6];             /* sha384 digest */
+          __u64 mrownerconfig[6];       /* sha348 digest */
+          __u64 reserved[43];           /* must be zero for future extensibility */
+  };
+
+
+KVM_TDX_INIT_VCPU
+-----------------
+:Type: vcpu ioctl
+
+Does additional VCPU initialization specific to TDX which corresponds to
+TDH.VP.INIT TDX SEAM call.
+
+- id: KVM_TDX_INIT_VCPU
+- flags: must be 0
+- data: initial value of the guest TD VCPU RCX
+- error: must be 0
+- unused: must be 0
+
+KVM_TDX_INIT_MEM_REGION
+-----------------------
+:Type: vm ioctl
+
+Encrypt a memory continuous region which corresponding to TDH.MEM.PAGE.ADD
+TDX SEAM call.
+If KVM_TDX_MEASURE_MEMORY_REGION flag is specified, it also extends measurement
+which corresponds to TDH.MR.EXTEND TDX SEAM call.
+
+- id: KVM_TDX_INIT_VCPU
+- flags: flags
+            currently only KVM_TDX_MEASURE_MEMORY_REGION is defined
+- data: pointer to struct kvm_tdx_init_mem_region
+- error: must be 0
+- unused: 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
+
+Complete measurement of the initial TD contents and mark it ready to run
+which corresponds to TDH.MR.FINALIZE
+
+- id: KVM_TDX_FINALIZE_VM
+- flags: must be 0
+- data: must be 0
+- error: must be 0
+- unused: must be 0
+
+KVM TDX creation flow
+=====================
+In addition to KVM normal flow, new TDX ioctls need to be called.  The control flow
+looks like as follows.
+
+#. system wide capability check
+  * KVM_CAP_VM_TYPES: check if VM type is supported and if TDX_VM_TYPE is
+    supported.
+
+#. creating VM
+  * KVM_CREATE_VM
+  * KVM_TDX_CAPABILITIES: query if TDX is supported on the platform.
+  * KVM_TDX_INIT_VM: pass TDX specific VM parameters.
+
+#. creating VCPU
+  * KVM_CREATE_VCPU
+  * KVM_TDX_INIT_VCPU: pass TDX specific VCPU parameters.
+
+#. initializing guest memory
+  * allocate guest memory and initialize page same to normal KVM case
+    In TDX case, parse and load TDVF into guest memory in addition.
+  * KVM_TDX_INIT_MEM_REGION to add and measure guest pages.
+    If the pages has contents above, those pages need to be added.
+    Otherwise the contents will be lost and guest sees zero pages.
+  * KVM_TDX_FINALIAZE_VM: Finalize VM and measurement
+    This must be after KVM_TDX_INIT_MEM_REGION.
+
+#. run vcpu
+
+Design discussion
+=================
+
+Coexistence of normal(VMX) VM and TD VM
+---------------------------------------
+It's required to allow both legacy(normal VMX) VMs and new TD VMs to
+coexist. Otherwise the benefits of VM flexibility would be eliminated.
+The main issue for it is that the logic of kvm_x86_ops callbacks for
+TDX is different from VMX. On the other hand, the variable,
+kvm_x86_ops, is global single variable. Not per-VM, not per-vcpu.
+
+Several points to be considered.
+  . No or minimal overhead when TDX is disabled(CONFIG_INTEL_TDX_HOST=n).
+  . Avoid overhead of indirect call via function pointers.
+  . Contain the changes under arch/x86/kvm/vmx directory and share logic
+    with VMX for maintenance.
+    Even though the ways to operation on VM (VMX instruction vs TDX
+    SEAM call) is different, the basic idea remains same. So, many
+    logic can be shared.
+  . Future maintenance
+    The huge change of kvm_x86_ops in (near) future isn't expected.
+    a centralized file is acceptable.
+
+- Wrapping kvm x86_ops: The current choice
+  Introduce dedicated file for arch/x86/kvm/vmx/main.c (the name,
+  main.c, is just chosen to show main entry points for callbacks.) and
+  wrapper functions around all the callbacks with
+  "if (is-tdx) tdx-callback() else vmx-callback()".
+
+  Pros:
+  - No major change in common x86 KVM code. The change is (mostly)
+    contained under arch/x86/kvm/vmx/.
+  - When TDX is disabled(CONFIG_INTEL_TDX_HOST=n), the overhead is
+    optimized out.
+  - Micro optimization by avoiding function pointer.
+  Cons:
+  - Many boiler plates in arch/x86/kvm/vmx/main.c.
+
+Alternative:
+- Introduce another callback layer under arch/x86/kvm/vmx.
+  Pros:
+  - No major change in common x86 KVM code. The change is (mostly)
+    contained under arch/x86/kvm/vmx/.
+  - clear separation on callbacks.
+  Cons:
+  - overhead in VMX even when TDX is disabled(CONFIG_INTEL_TDX_HOST=n).
+
+- Allow per-VM kvm_x86_ops callbacks instead of global kvm_x86_ops
+  Pros:
+  - clear separation on callbacks.
+  Cons:
+  - Big change in common x86 code.
+  - overhead in common code even when TDX is
+    disabled(CONFIG_INTEL_TDX_HOST=n).
+
+- Introduce new directory arch/x86/kvm/tdx
+  Pros:
+  - It clarifies that TDX is different from VMX.
+  Cons:
+  - Given the level of code sharing, it complicates code sharing.
+
+KVM MMU Changes
+---------------
+KVM MMU needs to be enhanced to handle Secure/Shared-EPT. The
+high-level execution flow is mostly same to normal EPT case.
+EPT violation/misconfiguration -> invoke TDP fault handler ->
+resolve TDP fault -> resume execution. (or emulate MMIO)
+The difference is, that S-EPT is operated(read/write) via TDX SEAM
+call which is expensive instead of direct read/write EPT entry.
+One bit of GPA (51 or 47 bit) is repurposed so that it means shared
+with host(if set to 1) or private to TD(if cleared to 0).
+
+- The current implementation
+  . Reuse the existing MMU code with minimal update.  Because the
+    execution flow is mostly same. But additional operation, TDX call
+    for S-EPT, is needed. So add hooks for it to kvm_x86_ops.
+  . For performance, minimize TDX SEAM call to operate on S-EPT. When
+    getting corresponding S-EPT pages/entry from faulting GPA, don't
+    use TDX SEAM call to read S-EPT entry. Instead create shadow copy
+    in host memory.
+    Repurpose the existing kvm_mmu_page as shadow copy of S-EPT and
+    associate S-EPT to it.
+  . Treats share bit as attributes. mask/unmask the bit where
+    necessary to keep the existing traversing code works.
+    Introduce kvm.arch.gfn_shared_mask and use "if (gfn_share_mask)"
+    for special case.
+    = 0 : for non-TDX case
+    = 51 or 47 bit set for TDX case.
+
+  Pros:
+  - Large code reuse with minimal new hooks.
+  - Execution path is same.
+  Cons:
+  - Complicates the existing code.
+  - Repurpose kvm_mmu_page as shadow of Secure-EPT can be confusing.
+
+Alternative:
+- Replace direct read/write on EPT entry with TDX-SEAM call by
+  introducing callbacks on EPT entry.
+  Pros:
+  - Straightforward.
+  Cons:
+  - Too many touching point.
+  - Too slow due to TDX-SEAM call.
+  - Overhead even when TDX is disabled(CONFIG_INTEL_TDX_HOST=n).
+
+- Sprinkle "if (is-tdx)" for TDX special case
+  Pros:
+  - Straightforward.
+  Cons:
+  - The result is non-generic and ugly.
+  - Put TDX specific logic into common KVM MMU code.
+
+New KVM API, ioctl (sub)command, to manage TD VMs
+-------------------------------------------------
+Additional KVM API are needed to control TD VMs. The operations on TD
+VMs are specific to TDX.
+
+- Piggyback and repurpose KVM_MEMORY_ENCRYPT_OP
+  Although not all operation isn't memory encryption, repupose to get
+  TDX specific ioctls.
+  Pros:
+  - No major change in common x86 KVM code.
+  Cons:
+  - The operations aren't actually memory encryption, but operations
+    on TD VMs.
+
+Alternative:
+- Introduce new ioctl for guest protection like
+  KVM_GUEST_PROTECTION_OP and introduce subcommand for TDX.
+  Pros:
+  - Clean name.
+  Cons:
+  - One more new ioctl for guest protection.
+  - Confusion with KVM_MEMORY_ENCRYPT_OP with KVM_GUEST_PROTECTION_OP.
+
+- Rename KVM_MEMORY_ENCRYPT_OP to KVM_GUEST_PROTECTION_OP and keep
+  KVM_MEMORY_ENCRYPT_OP as same value for user API for compatibility.
+  "#define KVM_MEMORY_ENCRYPT_OP KVM_GUEST_PROTECTION_OP" for uapi
+  compatibility.
+  Pros:
+  - No new ioctl with more suitable name.
+  Cons:
+  - May cause confusion to the existing user program.
+
+
+References
+==========
+
+.. [1] TDX specification
+   https://software.intel.com/content/www/us/en/develop/articles/intel-trust-domain-extensions.html
+.. [2] Intel Trust Domain Extensions (Intel TDX)
+   https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-whitepaper-final9-17.pdf
+.. [3] Intel CPU Architectural Extensions Specification
+   https://software.intel.com/content/dam/develop/external/us/en/documents/intel-tdx-cpu-architectural-specification.pdf
+.. [4] Intel TDX Module 1.0 EAS
+   https://software.intel.com/content/dam/develop/external/us/en/documents/intel-tdx-module-1eas.pdf
+.. [5] Intel TDX Loader Interface Specification
+   https://software.intel.com/content/dam/develop/external/us/en/documents/intel-tdx-seamldr-interface-specification.pdf
+.. [6] Intel TDX Guest-Hypervisor Communication Interface
+   https://software.intel.com/content/dam/develop/external/us/en/documents/intel-tdx-guest-hypervisor-communication-interface.pdf
+.. [7] Intel TDX Virtual Firmware Design Guide
+   https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-virtual-firmware-design-guide-rev-1.
+.. [8] intel public github
+   kvm TDX branch: https://github.com/intel/tdx/tree/kvm
+   TDX guest branch: https://github.com/intel/tdx/tree/guest
+.. [9] tdvf
+    https://github.com/tianocore/edk2-staging/tree/TDVF
+.. [10] KVM forum 2020: Intel Virtualization Technology Extensions to
+     Enable Hardware Isolated VMs
+     https://osseu2020.sched.com/event/eDzm/intel-virtualization-technology-extensions-to-enable-hardware-isolated-vms-sean-christopherson-intel
+.. [11] Linux Security Summit EU 2020:
+     Architectural Extensions for Hardware Virtual Machine Isolation
+     to Advance Confidential Computing in Public Clouds - Ravi Sahita
+     & Jun Nakajima, Intel Corporation
+     https://osseu2020.sched.com/event/eDOx/architectural-extensions-for-hardware-virtual-machine-isolation-to-advance-confidential-computing-in-public-clouds-ravi-sahita-jun-nakajima-intel-corporation
+.. [12] [RFCv2,00/16] KVM protected memory extension
+     https://lkml.org/lkml/2020/10/20/66
-- 
2.25.1