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Subject[PATCH v10 00/11] Add TDX Guest Support (Initial support)
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Hi All,

Intel's Trust Domain Extensions (TDX) protect guest VMs from malicious
hosts and some physical attacks. This series adds the basic TDX guest
infrastructure support (including #VE handler support, and #VE support
for halt and CPUID). This is just a subset of patches in the bare minimum
TDX support patch list which is required for supporting minimal
functional TDX guest. Other basic feature features like #VE support for
IO, MMIO, boot optimization fixes and shared-mm support will be submitted
in a separate patch set. To make reviewing easier we split it into smaller
series. This series alone is not necessarily fully functional.

Also, the host-side support patches, and support for advanced TD guest
features like attestation or debug-mode will be submitted at a later time.
Also, at this point it is not secure with some known holes in drivers, and
also hasn’t been fully audited and fuzzed yet.

TDX has a lot of similarities to SEV. It enhances confidentiality and
of guest memory and state (like registers) and includes a new exception
(#VE) for the same basic reasons as SEV-ES. Like SEV-SNP (not merged
yet), TDX limits the host's ability to effect changes in the guest
physical address space. With TDX the host cannot access the guest memory,
so various functionality that would normally be done in KVM has moved
into a (paravirtualized) guest. Partially this is done using the
Virtualization Exception (#VE) and partially with direct paravirtual hooks.

The TDX architecture also includes a new CPU mode called
Secure-Arbitration Mode (SEAM). The software (TDX module) running in this
mode arbitrates interactions between host and guest and implements many of
the guarantees of the TDX architecture.

Some of the key differences between TD and regular VM is,

1. Multi CPU bring-up is done using the ACPI MADT wake-up table.
2. A new #VE exception handler is added. The TDX module injects #VE exception
   to the guest TD in cases of instructions that need to be emulated, disallowed
   MSR accesses, etc.
3. By default memory is marked as private, and TD will selectively share it with
   VMM based on need.
   
Note that the kernel will also need to be hardened against low level inputs from
the now untrusted hosts. This will be done in follow on patches.

Please check the following info for more details about #VE on memory access:

== #VE on Memory Accesses ==

A TD guest is in control of whether its memory accesses are treated as
private or shared. It selects the behavior with a bit in its page table
entries.

=== #VE on Shared Pages ===

Accesses to shared mappings can cause #VE's. The hypervisor is in
control of when a #VE might occur, so the guest must be careful to only
reference shared pages when it is in a context that can safely handle a #VE.

However, shared mapping content can not be trusted since shared page
content is writable by the hypervisor. This means that shared mappings
are never used for sensitive memory contents like stacks or kernel text.
This means that the shared mapping property of inducing #VEs requires
essentially no special kernel handling in sensitive contexts like
syscall entry or NMIs.

=== #VE on Private Pages ===

Some accesses to private mappings may cause #VEs. Before a mapping is
accepted (aka. in the SEPT_PENDING state), a reference would cause
a #VE. But, after acceptance, references typically succeed.

The hypervisor can cause a private page reference to fail if it chooses
to move an accepted page to a "blocked" state. However, if it does
this, a page access will not generate a #VE. It will, instead, cause a
"TD Exit" where the hypervisor is required to handle the exception.

You can find TDX related documents in the following link.

https://software.intel.com/content/www/br/pt/develop/articles/intel-trust-domain-extensions.html

Changes since v9:
* Added inline definition of is_tdx_guest() for !CONFIG_INTEL_TDX_GUEST case

Changes since v8:
* * Change logs are include per patch.

Changes since v7:
* Included #VE details on memory access in cover letter.
* Change log is include per patch.

Changes since v6
* Fixed #ifdef format as per Boris comment in patch titled
"x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT".
* Fixed commit log of "x86/tdx: Handle CPUID via #VE" as per Dave
Hansen review comments.
* Removed TDX changes from "x86/tdx: Add protected guest support for
TDX guest" and created "x86/tdx: Add Intel version of
cc_platform_has()"
* Rebased on top of Tom Landecky's CC platform support patch series
https://lore.kernel.org/linux-iommu/f9951644147e27772bf4512325e8ba6472e363b7.1631141919.git.thomas.lendacky@amd.com/T/
* Rebased on top of v5.15-rc1.

Changes since v5:
* Moved patch titled "x86/tdx: Get TD execution environment
information via TDINFO" to the series which uses it.
* Rest of the change log is added per patch.

Changes since v4:
* Added a patch that adds TDX guest exception for CSTAR MSR.
* Rebased on top of Tom Lendacky's protected guest changes.
* Rest of the change log is added per patch.

Changes since v3:
* Moved generic protected guest changes from patch titled "x86:
Introduce generic protected guest abstraction" into seperate
patch outside this patchset. Also, TDX specific changes are
moved to patch titled "x86/tdx: Add protected guest support
for TDX guest"
* Rebased on top of v5.14-rc1.
* Rest of the change log is added per patch.

Changes since v1 (v2 is partial set submission):
* Patch titled "x86/x86: Add early_is_tdx_guest() interface" is moved
out of this series.
* Rest of the change log is added per patch.

Andi Kleen (1):
x86/tdx: Don't write CSTAR MSR on Intel

Kirill A. Shutemov (6):
x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT
x86/traps: Add #VE support for TDX guest
x86/tdx: Add HLT support for TDX guest
x86/tdx: Wire up KVM hypercalls
x86/tdx: Add MSR support for TDX guest
x86/tdx: Handle CPUID via #VE

Kuppuswamy Sathyanarayanan (4):
x86/tdx: Introduce INTEL_TDX_GUEST config option
x86/cpufeatures: Add TDX Guest CPU feature
x86/tdx: Add TDX support to intel_cc_platform_has()
x86/tdx: Add __tdx_module_call() and __tdx_hypercall() helper
functions

arch/x86/Kconfig | 15 ++
arch/x86/include/asm/asm-prototypes.h | 1 +
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/idtentry.h | 4 +
arch/x86/include/asm/irqflags.h | 44 ++--
arch/x86/include/asm/kvm_para.h | 22 ++
arch/x86/include/asm/paravirt.h | 20 +-
arch/x86/include/asm/paravirt_types.h | 3 +-
arch/x86/include/asm/tdx.h | 109 +++++++++
arch/x86/kernel/Makefile | 4 +
arch/x86/kernel/asm-offsets.c | 23 ++
arch/x86/kernel/cc_platform.c | 12 +-
arch/x86/kernel/cpu/common.c | 11 +-
arch/x86/kernel/head64.c | 9 +
arch/x86/kernel/idt.c | 3 +
arch/x86/kernel/paravirt.c | 3 +-
arch/x86/kernel/tdcall.S | 306 ++++++++++++++++++++++++++
arch/x86/kernel/tdx.c | 245 +++++++++++++++++++++
arch/x86/kernel/traps.c | 77 +++++++
include/linux/cc_platform.h | 9 +
20 files changed, 884 insertions(+), 37 deletions(-)
create mode 100644 arch/x86/include/asm/tdx.h
create mode 100644 arch/x86/kernel/tdcall.S
create mode 100644 arch/x86/kernel/tdx.c

--
2.25.1

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