Hi, Intel Trusted Domain Extensions (TDX) protects guest VMs from malicious host and certain physical attacks. This series provides support for initializing TDX in the host kernel. KVM support for TDX is being developed separately[1]. This series is based on Kirill's TDX guest series[2]. The reason is host side SEAMCALL implementation can share TDCALL's implementation which is implemented in TDX guest series. You can also find this series in below repo in github: https://github.com/intel/tdx/tree/host-upstream The code has been tested on couple of TDX-capable machines. I would consider it as ready for review (from overall design to detail implementations). It would be highly appreciated if anyone can help to review this series. For Intel folks, I would appreciate acks if the patches look good to you. Thanks in advance. Changelog history: RFC (v1): https://lore.kernel.org/all/e0ff030a49b252d91c789a89c303bb4206f85e3d.1646007267.git.kai.huang@xxxxxxxxx/T/ - RFC (v1) -> v2: - Rebased to Kirill's latest TDX guest code. - Fixed two issues that are related to finding all RAM memory regions based on e820. - Minor improvement on comments and commit messages. == Background == Intel Trusted Domain Extensions (TDX) protects guest VMs from malicious host and certain physical attacks. To support TDX, a new CPU mode called Secure Arbitration Mode (SEAM) is added to Intel processors. SEAM is an extension to the existing VMX architecture. It defines a new VMX root operation (SEAM VMX root) and a new VMX non-root operation (SEAM VMX non-root). SEAM VMX root operation is designed to host a CPU-attested, software module called the 'TDX module' which implements functions to manage crypto protected VMs called Trust Domains (TD). SEAM VMX root is also designed to host a CPU-attested, software module called the 'Intel Persistent SEAMLDR (Intel P-SEAMLDR)' to load and update the TDX module. Host kernel transits to either the P-SEAMLDR or the TDX module via a new SEAMCALL instruction. SEAMCALLs are host-side interface functions defined by the P-SEAMLDR and the TDX module around the new SEAMCALL instruction. They are similar to a hypercall, except they are made by host kernel to the SEAM software modules. TDX leverages Intel Multi-Key Total Memory Encryption (MKTME) to crypto protect TD guests. TDX reserves part of MKTME KeyID space as TDX private KeyIDs, which can only be used by software runs in SEAM. The physical address bits for encoding TDX private KeyID are treated as reserved bits when not in SEAM operation. The partitioning of MKTME KeyIDs and TDX private KeyIDs is configured by BIOS. Before being able to manage TD guests, the TDX module must be loaded and properly initialized using SEAMCALLs defined by TDX architecture. This series assumes both the P-SEAMLDR and the TDX module are loaded by BIOS before the kernel boots. There's no CPUID or MSR to detect either the P-SEAMLDR or the TDX module. Instead, detecting them can be done by using P-SEAMLDR's SEAMLDR.INFO SEAMCALL to detect P-SEAMLDR. The success of this SEAMCALL means the P-SEAMLDR is loaded. The P-SEAMLDR information returned by this SEAMCALL further tells whether TDX module is loaded. The TDX module is initialized in multiple steps: 1) Global initialization; 2) Logical-CPU scope initialization; 3) Enumerate the TDX module capabilities; 4) Configure the TDX module about usable memory ranges and global KeyID information; 5) Package-scope configuration for the global KeyID; 6) Initialize TDX metadata for usable memory ranges based on 4). Step 2) requires calling some SEAMCALL on all "BIOS-enabled" (in MADT table) logical cpus, otherwise step 4) will fail. Step 5) requires calling SEAMCALL on at least one cpu on all packages. TDX module can also be shut down at any time during module's lifetime, by calling SEAMCALL on all "BIOS-enabled" logical cpus. == Design Considerations == 1. Lazy TDX module initialization on-demand by caller None of the steps in the TDX module initialization process must be done during kernel boot. This series doesn't initialize TDX at boot time, but instead, provides two functions to allow caller to detect and initialize TDX on demand: if (tdx_detect()) goto no_tdx; if (tdx_init()) goto no_tdx; This approach has below pros: 1) Initializing the TDX module requires to reserve ~1/256th system RAM as metadata. Enabling TDX on demand allows only to consume this memory when TDX is truly needed (i.e. when KVM wants to create TD guests). 2) Both detecting and initializing the TDX module require calling SEAMCALL. However, SEAMCALL requires CPU being already in VMX operation (VMXON has been done). So far, KVM is the only user of TDX, and it already handles VMXON/VMXOFF. Therefore, letting KVM to initialize TDX on-demand avoids handling VMXON/VMXOFF (which is not that trivial) in core-kernel. Also, in long term, likely a reference based VMXON/VMXOFF approach is needed since more kernel components will need to handle VMXON/VMXONFF. 3) It is more flexible to support "TDX module runtime update" (not in this series). After updating to the new module at runtime, kernel needs to go through the initialization process again. For the new module, it's possible the metadata allocated for the old module cannot be reused for the new module, and needs to be re-allocated again. 2. Kernel policy on TDX memory Host kernel is responsible for choosing which memory regions can be used as TDX memory, and configuring those memory regions to the TDX module by using an array of "TD Memory Regions" (TDMR), which is a data structure defined by TDX architecture. The first generation of TDX essentially guarantees that all system RAM memory regions (excluding the memory below 1MB) can be used as TDX memory. To avoid having to modify the page allocator to distinguish TDX and non-TDX allocation, this series chooses to use all system RAM as TDX memory. E820 table is used to find all system RAM entries. Following e820__memblock_setup(), both E820_TYPE_RAM and E820_TYPE_RESERVED_KERN types are treated as TDX memory, and contiguous ranges in the same NUMA node are merged together (similar to memblock_add()) before trimming the non-page-aligned part. X86 Legacy PMEMs (E820_TYPE_PRAM) also unconditionally treated as TDX memory as underneath they are RAM and can be potentially used as TD guest memory. Memblock is not used to find all RAM regions as: 1) it is gone after kernel boots; 2) it doesn't have legacy PMEM. 3. Memory hotplug The first generation of TDX architecturally doesn't support memory hotplug. And the first generation of TDX-capable platforms don't support physical memory hotplug. Since it physically cannot happen, this series doesn't add any check in ACPI memory hotplug code path to disable it. A special case of memory hotplug is adding NVDIMM as system RAM using kmem driver. However the first generation of TDX-capable platforms cannot enable TDX and NVDIMM simultaneously, so in practice this cannot happen either. Another case is admin can use 'memmap' kernel command line to create legacy PMEMs and use them as TD guest memory, or theoretically, can use kmem driver to add them as system RAM. To avoid having to change memory hotplug code to prevent this from happening, this series always include legacy PMEMs when constructing TDMRs so they are also TDX memory. 4. CPU hotplug The first generation of TDX architecturally doesn't support ACPI CPU hotplug. All logical cpus are enabled by BIOS in MADT table. Also, the first generation of TDX-capable platforms don't support ACPI CPU hotplug either. Since this physically cannot happen, this series doesn't add any check in ACPI CPU hotplug code path to disable it. Also, only TDX module initialization requires all BIOS-enabled cpus are online. After the initialization, any logical cpu can be brought down and brought up to online again later. Therefore this series doesn't change logical CPU hotplug either. 5. TDX interaction with kexec() If TDX is ever enabled and/or used to run any TD guests, the cachelines of TDX private memory, including PAMTs, used by TDX module need to be flushed before transiting to the new kernel otherwise they may silently corrupt the new kernel. Similar to SME, this series flushes cache in stop_this_cpu(). The TDX module can be initialized only once during its lifetime. The first generation of TDX doesn't have interface to reset TDX module to uninitialized state so it can be initialized again. This implies: - If the old kernel fails to initialize TDX, the new kernel cannot use TDX too unless the new kernel fixes the bug which leads to initialization failure in the old kernel and can resume from where the old kernel stops. This requires certain coordination between the two kernels. - If the old kernel has initialized TDX successfully, the new kernel may be able to use TDX if the two kernels have the exactly same configurations on the TDX module. It further requires the new kernel to reserve the TDX metadata pages (allocated by the old kernel) in its page allocator. It also requires coordination between the two kernels. Furthermore, if kexec() is done when there are active TD guests running, the new kernel cannot use TDX because it's extremely hard for the old kernel to pass all TDX private pages to the new kernel. Given that, this series doesn't support TDX after kexec() (except the old kernel doesn't attempt to initialize TDX at all). And this series doesn't shut down TDX module but leaves it open during kexec(). It is because shutting down TDX module requires CPU being in VMX operation but there's no guarantee of this during kexec(). Leaving the TDX module open is not the best case, but it is OK since the new kernel won't be able to use TDX anyway (therefore TDX module won't run at all). [1] https://lore.kernel.org/lkml/772b20e270b3451aea9714260f2c40ddcc4afe80.1646422845.git.isaku.yamahata@xxxxxxxxx/T/ [2] https://github.com/intel/tdx/tree/guest-upstream Kai Huang (21): x86/virt/tdx: Detect SEAM x86/virt/tdx: Detect TDX private KeyIDs x86/virt/tdx: Implement the SEAMCALL base function x86/virt/tdx: Add skeleton for detecting and initializing TDX on demand x86/virt/tdx: Detect P-SEAMLDR and TDX module x86/virt/tdx: Shut down TDX module in case of error x86/virt/tdx: Do TDX module global initialization x86/virt/tdx: Do logical-cpu scope TDX module initialization x86/virt/tdx: Get information about TDX module and convertible memory x86/virt/tdx: Add placeholder to coveret all system RAM as TDX memory x86/virt/tdx: Choose to use all system RAM as TDX memory x86/virt/tdx: Create TDMRs to cover all system RAM x86/virt/tdx: Allocate and set up PAMTs for TDMRs x86/virt/tdx: Set up reserved areas for all TDMRs x86/virt/tdx: Reserve TDX module global KeyID x86/virt/tdx: Configure TDX module with TDMRs and global KeyID x86/virt/tdx: Configure global KeyID on all packages x86/virt/tdx: Initialize all TDMRs x86: Flush cache of TDX private memory during kexec() x86/virt/tdx: Add kernel command line to opt-in TDX host support Documentation/x86: Add documentation for TDX host support .../admin-guide/kernel-parameters.txt | 6 + Documentation/x86/index.rst | 1 + Documentation/x86/tdx_host.rst | 300 +++ arch/x86/Kconfig | 14 + arch/x86/Makefile | 2 + arch/x86/include/asm/tdx.h | 15 + arch/x86/kernel/cpu/intel.c | 3 + arch/x86/kernel/process.c | 15 +- arch/x86/virt/Makefile | 2 + arch/x86/virt/vmx/Makefile | 2 + arch/x86/virt/vmx/seamcall.S | 52 + arch/x86/virt/vmx/tdx.c | 1711 +++++++++++++++++ arch/x86/virt/vmx/tdx.h | 137 ++ 13 files changed, 2259 insertions(+), 1 deletion(-) create mode 100644 Documentation/x86/tdx_host.rst create mode 100644 arch/x86/virt/Makefile create mode 100644 arch/x86/virt/vmx/Makefile create mode 100644 arch/x86/virt/vmx/seamcall.S create mode 100644 arch/x86/virt/vmx/tdx.c create mode 100644 arch/x86/virt/vmx/tdx.h -- 2.35.1
