KVM: x86: Add a #define for the architectural max instruction length

Add a #define to capture x86's architecturally defined max instruction
length instead of open coding the literal in a variety of places.

No functional change intended.

Link: https://lore.kernel.org/r/20250201015518.689704-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/kvm_emulate.h

@@ -275,8 +275,10 @@ struct operand {
 	};
 };
 
+#define X86_MAX_INSTRUCTION_LENGTH	15
+
 struct fetch_cache {
-	u8 data[15];
+	u8 data[X86_MAX_INSTRUCTION_LENGTH];
 	u8 *ptr;
 	u8 *end;
 };

arch/x86/kvm/trace.h

@@ -830,12 +830,12 @@ TRACE_EVENT(kvm_emulate_insn,
 	TP_ARGS(vcpu, failed),
 
 	TP_STRUCT__entry(
-		__field(    __u64, rip                       )
-		__field(    __u32, csbase                    )
-		__field(    __u8,  len                       )
-		__array(    __u8,  insn,    15	             )
-		__field(    __u8,  flags       	   	     )
-		__field(    __u8,  failed                    )
+		__field(    __u64, rip                              )
+		__field(    __u32, csbase                           )
+		__field(    __u8,  len                              )
+		__array(    __u8,  insn, X86_MAX_INSTRUCTION_LENGTH )
+		__field(    __u8,  flags       	   	            )
+		__field(    __u8,  failed                           )
 		),
 
 	TP_fast_assign(
@@ -846,7 +846,7 @@ TRACE_EVENT(kvm_emulate_insn,
 		__entry->rip = vcpu->arch.emulate_ctxt->_eip - __entry->len;
 		memcpy(__entry->insn,
 		       vcpu->arch.emulate_ctxt->fetch.data,
-		       15);
+		       X86_MAX_INSTRUCTION_LENGTH);
 		__entry->flags = kei_decode_mode(vcpu->arch.emulate_ctxt->mode);
 		__entry->failed = failed;
 		),

arch/x86/kvm/vmx/nested.c

@@ -2970,7 +2970,7 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
 		case INTR_TYPE_SOFT_EXCEPTION:
 		case INTR_TYPE_SOFT_INTR:
 		case INTR_TYPE_PRIV_SW_EXCEPTION:
-			if (CC(vmcs12->vm_entry_instruction_len > 15) ||
+			if (CC(vmcs12->vm_entry_instruction_len > X86_MAX_INSTRUCTION_LENGTH) ||
 			    CC(vmcs12->vm_entry_instruction_len == 0 &&
 			    CC(!nested_cpu_has_zero_length_injection(vcpu))))
 				return -EINVAL;