1 files changed, 57 insertions, 1 deletions

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 00ff0a830970..50c3b97d6db7 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -180,6 +180,48 @@ static bool write_msr(struct pt_regs *regs)
 	return !__tdx_hypercall(&args, 0);
 }
 
+static bool handle_cpuid(struct pt_regs *regs)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = hcall_func(EXIT_REASON_CPUID),
+		.r12 = regs->ax,
+		.r13 = regs->cx,
+	};
+
+	/*
+	 * Only allow VMM to control range reserved for hypervisor
+	 * communication.
+	 *
+	 * Return all-zeros for any CPUID outside the range. It matches CPU
+	 * behaviour for non-supported leaf.
+	 */
+	if (regs->ax < 0x40000000 || regs->ax > 0x4FFFFFFF) {
+		regs->ax = regs->bx = regs->cx = regs->dx = 0;
+		return true;
+	}
+
+	/*
+	 * Emulate the CPUID instruction via a hypercall. More info about
+	 * ABI can be found in TDX Guest-Host-Communication Interface
+	 * (GHCI), section titled "VP.VMCALL<Instruction.CPUID>".
+	 */
+	if (__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT))
+		return false;
+
+	/*
+	 * As per TDX GHCI CPUID ABI, r12-r15 registers contain contents of
+	 * EAX, EBX, ECX, EDX registers after the CPUID instruction execution.
+	 * So copy the register contents back to pt_regs.
+	 */
+	regs->ax = args.r12;
+	regs->bx = args.r13;
+	regs->cx = args.r14;
+	regs->dx = args.r15;
+
+	return true;
+}
+
 void tdx_get_ve_info(struct ve_info *ve)
 {
 	struct tdx_module_output out;
@@ -210,6 +252,18 @@ void tdx_get_ve_info(struct ve_info *ve)
 	ve->instr_info  = upper_32_bits(out.r10);
 }
 
+/* Handle the user initiated #VE */
+static bool virt_exception_user(struct pt_regs *regs, struct ve_info *ve)
+{
+	switch (ve->exit_reason) {
+	case EXIT_REASON_CPUID:
+		return handle_cpuid(regs);
+	default:
+		pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
+		return false;
+	}
+}
+
 /* Handle the kernel #VE */
 static bool virt_exception_kernel(struct pt_regs *regs, struct ve_info *ve)
 {
@@ -220,6 +274,8 @@ static bool virt_exception_kernel(struct pt_regs *regs, struct ve_info *ve)
 		return read_msr(regs);
 	case EXIT_REASON_MSR_WRITE:
 		return write_msr(regs);
+	case EXIT_REASON_CPUID:
+		return handle_cpuid(regs);
 	default:
 		pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
 		return false;
@@ -231,7 +287,7 @@ bool tdx_handle_virt_exception(struct pt_regs *regs, struct ve_info *ve)
 	bool ret;
 
 	if (user_mode(regs))
-		ret = false;
+		ret = virt_exception_user(regs, ve);
 	else
 		ret = virt_exception_kernel(regs, ve);