[PATCHv3 11/32] x86/tdx: Handle CPUID via #VE

[Kirill A. Shutemov]

In TDX guests, most CPUID leaf/sub-leaf combinations are virtualized
by the TDX module while some trigger #VE.

Implement the #VE handling for EXIT_REASON_CPUID by handing it through
the hypercall, which in turn lets the TDX module handle it by invoking
the host VMM.

More details on CPUID Virtualization can be found in the TDX module
specification, the section titled "CPUID Virtualization".

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/coco/tdx.c | 41 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/arch/x86/coco/tdx.c b/arch/x86/coco/tdx.c
index c0549dce2588..83cbc94b30d0 100644
--- a/arch/x86/coco/tdx.c
+++ b/arch/x86/coco/tdx.c
@@ -154,6 +154,36 @@ 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 = EXIT_REASON_CPUID,
+		.r12 = regs->ax,
+		.r13 = regs->cx,
+	};
+
+	/*
+	 * 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;
@@ -186,8 +216,13 @@ void tdx_get_ve_info(struct ve_info *ve)
  */
 static bool virt_exception_user(struct pt_regs *regs, struct ve_info *ve)
 {
-	pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
-	return false;
+	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 */
@@ -200,6 +235,8 @@ 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;
-- 
2.34.1