[PATCH 0/4] KVM: TDX: Cleanup the kvm_x86_ops structure for vmx/tdx

Vishal Verma
2025-03-13T19:30:28Z

This is a cleanup that should follow the initial TDX base support (i.e.
not an immediate fix needed for kvm-coco-queue).

In [1], Sean points out that the kvm_x86_ops structure and its
associated helpers and wrappers can be cleaned up a lot by -

1. Putting the wrappers under CONFIG_KVM_INTEL_TDX, and
2. Defining the helpers with macros that switch between the tdx and
non-tdx case, as well as NULL out the TDX-only stubs when needed.

This cleans up the generated code by completely removing trampolines
that would otherwise be left behind in the CONFIG_KVM_INTEL_TDX=n case.

[1]: https://lore.kernel.org/kvm/Z6v9yjWLNTU6X90d@google.com/

For example, looking at vt_refresh_apicv_exec_ctrl(), before this cleanup,
when CONFIG_KVM_INTEL_TDX=n, the following asm is generated:

0000000000036490 <vt_refresh_apicv_exec_ctrl>:
36490: f3 0f 1e fa endbr64
36494: e8 00 00 00 00 call 36499 <vt_refresh_apicv_exec_ctrl+0x9>
36495: R_X86_64_PLT32 __fentry__-0x4
36499: e9 00 00 00 00 jmp 3649e <vt_refresh_apicv_exec_ctrl+0xe>
3649a: R_X86_64_PLT32 vmx_refresh_apicv_exec_ctrl-0x4
3649e: 66 90 xchg %ax,%ax

But with these patches, it goes away completely.

These patches have been tested with TDX kvm-unit-tests, booting a Linux
TD, TDX enhanced KVM selftests, and building and examining the generated
assembly (or lack thereof) with both CONFIG_KVM_INTEL_TDX=y and
CONFIG_KVM_INTEL_TDX=n

Based on a patch by Sean Christopherson <seanjc@google.com>

Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
Vishal Verma (4):
KVM: TDX: Move apicv_pre_state_restore to posted_intr.c
KVM: VMX: Move x86_ops wrappers under CONFIG_KVM_INTEL_TDX
KVM: VMX: Make naming consistent for kvm_complete_insn_gp via define
KVM: VMX: Clean up and macrofy x86_ops

arch/x86/kvm/vmx/posted_intr.h | 1 +
arch/x86/kvm/vmx/tdx.h | 2 +-
arch/x86/kvm/vmx/x86_ops.h | 68 +-------------
arch/x86/kvm/vmx/main.c | 204 ++++++++++++++++++++---------------------
arch/x86/kvm/vmx/posted_intr.c | 8 ++
5 files changed, 113 insertions(+), 170 deletions(-)
---
base-commit: 85c9490bbed74b006a614e542da404a55ff5938f
change-id: 20250311-vverma7-cleanup_x86_ops-c62e50e47126

Best regards,
--
Vishal Verma <vishal.l.verma@intel.com>