[PATCH v2 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

[Kuppuswamy Sathyanarayanan]

In non-root TDX guest mode, MWAIT, MONITOR and WBINVD instructions
are not supported. So handle #VE due to these instructions as no ops.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
---

Changes since v1:
 * Added WARN() for MWAIT #VE exception.

Changes since previous series:
 * Suppressed MWAIT feature as per Andi's comment.
 * Added warning debug log for MWAIT #VE exception.

 arch/x86/kernel/tdx.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index e936b2f88bf6..3c6158a53c17 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -308,6 +308,9 @@ void __init tdx_early_init(void)
 
 	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
 
+	/* MWAIT is not supported in TDX platform, so suppress it */
+	setup_clear_cpu_cap(X86_FEATURE_MWAIT);
+
 	tdg_get_info();
 
 	pv_ops.irq.safe_halt = tdg_safe_halt;
@@ -362,6 +365,26 @@ int tdg_handle_virtualization_exception(struct pt_regs *regs,
 	case EXIT_REASON_EPT_VIOLATION:
 		ve->instr_len = tdg_handle_mmio(regs, ve);
 		break;
+	/*
+	 * Per Guest-Host-Communication Interface (GHCI) for Intel Trust
+	 * Domain Extensions (Intel TDX) specification, sec 2.4,
+	 * some instructions that unconditionally cause #VE (such as WBINVD,
+	 * MONITOR, MWAIT) do not have corresponding TDCALL
+	 * [TDG.VP.VMCALL <Instruction>] leaves, since the TD has been designed
+	 * with no deterministic way to confirm the result of those operations
+	 * performed by the host VMM.  In those cases, the goal is for the TD
+	 * #VE handler to increment the RIP appropriately based on the VE
+	 * information provided via TDCALL.
+	 */
+	case EXIT_REASON_WBINVD:
+		pr_warn_once("WBINVD #VE Exception\n");
+	case EXIT_REASON_MONITOR_INSTRUCTION:
+		/* Handle as nops. */
+		break;
+	case EXIT_REASON_MWAIT_INSTRUCTION:
+		/* MWAIT is supressed, not supposed to reach here. */
+		WARN(1, "MWAIT unexpected #VE Exception\n");
+		return -EFAULT;
 	default:
 		pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
 		return -EFAULT;
-- 
2.25.1