Merge tag 'x86_tdx_for_6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 TDX updates from Dave Hansen:
 "This contains the initial support for host-side TDX support so that
  KVM can run TDX-protected guests. This does not include the actual
  KVM-side support which will come from the KVM folks. The TDX host
  interactions with kexec also needs to be ironed out before this is
  ready for prime time, so this code is currently Kconfig'd off when
  kexec is on.

  The majority of the code here is the kernel telling the TDX module
  which memory to protect and handing some additional memory over to it
  to use to store TDX module metadata. That sounds pretty simple, but
  the TDX architecture is rather flexible and it takes quite a bit of
  back-and-forth to say, "just protect all memory, please."

  There is also some code tacked on near the end of the series to handle
  a hardware erratum. The erratum can make software bugs such as a
  kernel write to TDX-protected memory cause a machine check and
  masquerade as a real hardware failure. The erratum handling watches
  out for these and tries to provide nicer user errors"

* tag 'x86_tdx_for_6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
  x86/virt/tdx: Make TDX host depend on X86_MCE
  x86/virt/tdx: Disable TDX host support when kexec is enabled
  Documentation/x86: Add documentation for TDX host support
  x86/mce: Differentiate real hardware #MCs from TDX erratum ones
  x86/cpu: Detect TDX partial write machine check erratum
  x86/virt/tdx: Handle TDX interaction with sleep and hibernation
  x86/virt/tdx: Initialize all TDMRs
  x86/virt/tdx: Configure global KeyID on all packages
  x86/virt/tdx: Configure TDX module with the TDMRs and global KeyID
  x86/virt/tdx: Designate reserved areas for all TDMRs
  x86/virt/tdx: Allocate and set up PAMTs for TDMRs
  x86/virt/tdx: Fill out TDMRs to cover all TDX memory regions
  x86/virt/tdx: Add placeholder to construct TDMRs to cover all TDX memory regions
  x86/virt/tdx: Get module global metadata for module initialization
  x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory
  x86/virt/tdx: Add skeleton to enable TDX on demand
  x86/virt/tdx: Add SEAMCALL error printing for module initialization
  x86/virt/tdx: Handle SEAMCALL no entropy error in common code
  x86/virt/tdx: Make INTEL_TDX_HOST depend on X86_X2APIC
  x86/virt/tdx: Define TDX supported page sizes as macros
  ...

1 files changed, 196 insertions, 11 deletions

diff --git a/Documentation/arch/x86/tdx.rst b/Documentation/arch/x86/tdx.rst
index dc8d9fd2c3f7..719043cd8b46 100644
--- a/Documentation/arch/x86/tdx.rst
+++ b/Documentation/arch/x86/tdx.rst
@@ -10,6 +10,191 @@ encrypting the guest memory. In TDX, a special module running in a special
 mode sits between the host and the guest and manages the guest/host
 separation.
 
+TDX Host Kernel Support
+=======================
+
+TDX introduces a new CPU mode called Secure Arbitration Mode (SEAM) and
+a new isolated range pointed by the SEAM Ranger Register (SEAMRR).  A
+CPU-attested software module called 'the TDX module' runs inside the new
+isolated range to provide the functionalities to manage and run protected
+VMs.
+
+TDX also leverages Intel Multi-Key Total Memory Encryption (MKTME) to
+provide crypto-protection to the VMs.  TDX reserves part of MKTME KeyIDs
+as TDX private KeyIDs, which are only accessible within the SEAM mode.
+BIOS is responsible for partitioning legacy MKTME KeyIDs and TDX KeyIDs.
+
+Before the TDX module can be used to create and run protected VMs, it
+must be loaded into the isolated range and properly initialized.  The TDX
+architecture doesn't require the BIOS to load the TDX module, but the
+kernel assumes it is loaded by the BIOS.
+
+TDX boot-time detection
+-----------------------
+
+The kernel detects TDX by detecting TDX private KeyIDs during kernel
+boot.  Below dmesg shows when TDX is enabled by BIOS::
+
+  [..] virt/tdx: BIOS enabled: private KeyID range: [16, 64)
+
+TDX module initialization
+---------------------------------------
+
+The kernel talks to the TDX module via the new SEAMCALL instruction.  The
+TDX module implements SEAMCALL leaf functions to allow the kernel to
+initialize it.
+
+If the TDX module isn't loaded, the SEAMCALL instruction fails with a
+special error.  In this case the kernel fails the module initialization
+and reports the module isn't loaded::
+
+  [..] virt/tdx: module not loaded
+
+Initializing the TDX module consumes roughly ~1/256th system RAM size to
+use it as 'metadata' for the TDX memory.  It also takes additional CPU
+time to initialize those metadata along with the TDX module itself.  Both
+are not trivial.  The kernel initializes the TDX module at runtime on
+demand.
+
+Besides initializing the TDX module, a per-cpu initialization SEAMCALL
+must be done on one cpu before any other SEAMCALLs can be made on that
+cpu.
+
+The kernel provides two functions, tdx_enable() and tdx_cpu_enable() to
+allow the user of TDX to enable the TDX module and enable TDX on local
+cpu respectively.
+
+Making SEAMCALL requires VMXON has been done on that CPU.  Currently only
+KVM implements VMXON.  For now both tdx_enable() and tdx_cpu_enable()
+don't do VMXON internally (not trivial), but depends on the caller to
+guarantee that.
+
+To enable TDX, the caller of TDX should: 1) temporarily disable CPU
+hotplug; 2) do VMXON and tdx_enable_cpu() on all online cpus; 3) call
+tdx_enable().  For example::
+
+        cpus_read_lock();
+        on_each_cpu(vmxon_and_tdx_cpu_enable());
+        ret = tdx_enable();
+        cpus_read_unlock();
+        if (ret)
+                goto no_tdx;
+        // TDX is ready to use
+
+And the caller of TDX must guarantee the tdx_cpu_enable() has been
+successfully done on any cpu before it wants to run any other SEAMCALL.
+A typical usage is do both VMXON and tdx_cpu_enable() in CPU hotplug
+online callback, and refuse to online if tdx_cpu_enable() fails.
+
+User can consult dmesg to see whether the TDX module has been initialized.
+
+If the TDX module is initialized successfully, dmesg shows something
+like below::
+
+  [..] virt/tdx: 262668 KBs allocated for PAMT
+  [..] virt/tdx: module initialized
+
+If the TDX module failed to initialize, dmesg also shows it failed to
+initialize::
+
+  [..] virt/tdx: module initialization failed ...
+
+TDX Interaction to Other Kernel Components
+------------------------------------------
+
+TDX Memory Policy
+~~~~~~~~~~~~~~~~~
+
+TDX reports a list of "Convertible Memory Region" (CMR) to tell the
+kernel which memory is TDX compatible.  The kernel needs to build a list
+of memory regions (out of CMRs) as "TDX-usable" memory and pass those
+regions to the TDX module.  Once this is done, those "TDX-usable" memory
+regions are fixed during module's lifetime.
+
+To keep things simple, currently the kernel simply guarantees all pages
+in the page allocator are TDX memory.  Specifically, the kernel uses all
+system memory in the core-mm "at the time of TDX module initialization"
+as TDX memory, and in the meantime, refuses to online any non-TDX-memory
+in the memory hotplug.
+
+Physical Memory Hotplug
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Note TDX assumes convertible memory is always physically present during
+machine's runtime.  A non-buggy BIOS should never support hot-removal of
+any convertible memory.  This implementation doesn't handle ACPI memory
+removal but depends on the BIOS to behave correctly.
+
+CPU Hotplug
+~~~~~~~~~~~
+
+TDX module requires the per-cpu initialization SEAMCALL must be done on
+one cpu before any other SEAMCALLs can be made on that cpu.  The kernel
+provides tdx_cpu_enable() to let the user of TDX to do it when the user
+wants to use a new cpu for TDX task.
+
+TDX doesn't support physical (ACPI) CPU hotplug.  During machine boot,
+TDX verifies all boot-time present logical CPUs are TDX compatible before
+enabling TDX.  A non-buggy BIOS should never support hot-add/removal of
+physical CPU.  Currently the kernel doesn't handle physical CPU hotplug,
+but depends on the BIOS to behave correctly.
+
+Note TDX works with CPU logical online/offline, thus the kernel still
+allows to offline logical CPU and online it again.
+
+Kexec()
+~~~~~~~
+
+TDX host support currently lacks the ability to handle kexec.  For
+simplicity only one of them can be enabled in the Kconfig.  This will be
+fixed in the future.
+
+Erratum
+~~~~~~~
+
+The first few generations of TDX hardware have an erratum.  A partial
+write to a TDX private memory cacheline will silently "poison" the
+line.  Subsequent reads will consume the poison and generate a machine
+check.
+
+A partial write is a memory write where a write transaction of less than
+cacheline lands at the memory controller.  The CPU does these via
+non-temporal write instructions (like MOVNTI), or through UC/WC memory
+mappings.  Devices can also do partial writes via DMA.
+
+Theoretically, a kernel bug could do partial write to TDX private memory
+and trigger unexpected machine check.  What's more, the machine check
+code will present these as "Hardware error" when they were, in fact, a
+software-triggered issue.  But in the end, this issue is hard to trigger.
+
+If the platform has such erratum, the kernel prints additional message in
+machine check handler to tell user the machine check may be caused by
+kernel bug on TDX private memory.
+
+Interaction vs S3 and deeper states
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+TDX cannot survive from S3 and deeper states.  The hardware resets and
+disables TDX completely when platform goes to S3 and deeper.  Both TDX
+guests and the TDX module get destroyed permanently.
+
+The kernel uses S3 for suspend-to-ram, and use S4 and deeper states for
+hibernation.  Currently, for simplicity, the kernel chooses to make TDX
+mutually exclusive with S3 and hibernation.
+
+The kernel disables TDX during early boot when hibernation support is
+available::
+
+  [..] virt/tdx: initialization failed: Hibernation support is enabled
+
+Add 'nohibernate' kernel command line to disable hibernation in order to
+use TDX.
+
+ACPI S3 is disabled during kernel early boot if TDX is enabled.  The user
+needs to turn off TDX in the BIOS in order to use S3.
+
+TDX Guest Support
+=================
 Since the host cannot directly access guest registers or memory, much
 normal functionality of a hypervisor must be moved into the guest. This is
 implemented using a Virtualization Exception (#VE) that is handled by the
@@ -20,7 +205,7 @@ TDX includes new hypercall-like mechanisms for communicating from the
 guest to the hypervisor or the TDX module.
 
 New TDX Exceptions
-==================
+------------------
 
 TDX guests behave differently from bare-metal and traditional VMX guests.
 In TDX guests, otherwise normal instructions or memory accesses can cause
@@ -30,7 +215,7 @@ Instructions marked with an '*' conditionally cause exceptions.  The
 details for these instructions are discussed below.
 
 Instruction-based #VE
----------------------
+~~~~~~~~~~~~~~~~~~~~~
 
 - Port I/O (INS, OUTS, IN, OUT)
 - HLT
@@ -41,7 +226,7 @@ Instruction-based #VE
 - CPUID*
 
 Instruction-based #GP
----------------------
+~~~~~~~~~~~~~~~~~~~~~
 
 - All VMX instructions: INVEPT, INVVPID, VMCLEAR, VMFUNC, VMLAUNCH,
   VMPTRLD, VMPTRST, VMREAD, VMRESUME, VMWRITE, VMXOFF, VMXON
@@ -52,7 +237,7 @@ Instruction-based #GP
 - RDMSR*,WRMSR*
 
 RDMSR/WRMSR Behavior
---------------------
+~~~~~~~~~~~~~~~~~~~~
 
 MSR access behavior falls into three categories:
 
@@ -73,7 +258,7 @@ trapping and handling in the TDX module.  Other than possibly being slow,
 these MSRs appear to function just as they would on bare metal.
 
 CPUID Behavior
---------------
+~~~~~~~~~~~~~~
 
 For some CPUID leaves and sub-leaves, the virtualized bit fields of CPUID
 return values (in guest EAX/EBX/ECX/EDX) are configurable by the
@@ -93,7 +278,7 @@ not know how to handle. The guest kernel may ask the hypervisor for the
 value with a hypercall.
 
 #VE on Memory Accesses
-======================
+----------------------
 
 There are essentially two classes of TDX memory: private and shared.
 Private memory receives full TDX protections.  Its content is protected
@@ -107,7 +292,7 @@ entries.  This helps ensure that a guest does not place sensitive
 information in shared memory, exposing it to the untrusted hypervisor.
 
 #VE on Shared Memory
---------------------
+~~~~~~~~~~~~~~~~~~~~
 
 Access to shared mappings can cause a #VE.  The hypervisor ultimately
 controls whether a shared memory access causes a #VE, so the guest must be
@@ -127,7 +312,7 @@ be careful not to access device MMIO regions unless it is also prepared to
 handle a #VE.
 
 #VE on Private Pages
---------------------
+~~~~~~~~~~~~~~~~~~~~
 
 An access to private mappings can also cause a #VE.  Since all kernel
 memory is also private memory, the kernel might theoretically need to
@@ -145,7 +330,7 @@ The hypervisor is permitted to unilaterally move accepted pages to a
 to handle the exception.
 
 Linux #VE handler
-=================
+-----------------
 
 Just like page faults or #GP's, #VE exceptions can be either handled or be
 fatal.  Typically, an unhandled userspace #VE results in a SIGSEGV.
@@ -167,7 +352,7 @@ While the block is in place, any #VE is elevated to a double fault (#DF)
 which is not recoverable.
 
 MMIO handling
-=============
+-------------
 
 In non-TDX VMs, MMIO is usually implemented by giving a guest access to a
 mapping which will cause a VMEXIT on access, and then the hypervisor
@@ -189,7 +374,7 @@ MMIO access via other means (like structure overlays) may result in an
 oops.
 
 Shared Memory Conversions
-=========================
+-------------------------
 
 All TDX guest memory starts out as private at boot.  This memory can not
 be accessed by the hypervisor.  However, some kernel users like device