KVM: nVMX: Use macros and #defines in vmx_restore_vmx_misc()

Use macros in vmx_restore_vmx_misc() instead of open coding everything
using BIT_ULL() and GENMASK_ULL().  Opportunistically split feature bits
and reserved bits into separate variables, and add a comment explaining
the subset logic (it's not immediately obvious that the set of feature
bits is NOT the set of _supported_ feature bits).

Cc: Shan Kang <shan.kang@intel.com>
Cc: Kai Huang <kai.huang@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
[sean: split to separate patch, write changelog, drop #defines]
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20240605231918.2915961-11-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/vmx/nested.c

@@ -1345,16 +1345,29 @@ vmx_restore_control_msr(struct vcpu_vmx *vmx, u32 msr_index, u64 data)
 
 static int vmx_restore_vmx_misc(struct vcpu_vmx *vmx, u64 data)
 {
-	const u64 feature_and_reserved_bits =
-		/* feature */
-		BIT_ULL(5) | GENMASK_ULL(8, 6) | BIT_ULL(14) | BIT_ULL(15) |
-		BIT_ULL(28) | BIT_ULL(29) | BIT_ULL(30) |
-		/* reserved */
-		GENMASK_ULL(13, 9) | BIT_ULL(31);
+	const u64 feature_bits = VMX_MISC_SAVE_EFER_LMA |
+				 VMX_MISC_ACTIVITY_HLT |
+				 VMX_MISC_ACTIVITY_SHUTDOWN |
+				 VMX_MISC_ACTIVITY_WAIT_SIPI |
+				 VMX_MISC_INTEL_PT |
+				 VMX_MISC_RDMSR_IN_SMM |
+				 VMX_MISC_VMWRITE_SHADOW_RO_FIELDS |
+				 VMX_MISC_VMXOFF_BLOCK_SMI |
+				 VMX_MISC_ZERO_LEN_INS;
+
+	const u64 reserved_bits = BIT_ULL(31) | GENMASK_ULL(13, 9);
+
 	u64 vmx_misc = vmx_control_msr(vmcs_config.nested.misc_low,
 				       vmcs_config.nested.misc_high);
 
-	if (!is_bitwise_subset(vmx_misc, data, feature_and_reserved_bits))
+	BUILD_BUG_ON(feature_bits & reserved_bits);
+
+	/*
+	 * The incoming value must not set feature bits or reserved bits that
+	 * aren't allowed/supported by KVM.  Fields, i.e. multi-bit values, are
+	 * explicitly checked below.
+	 */
+	if (!is_bitwise_subset(vmx_misc, data, feature_bits | reserved_bits))
 		return -EINVAL;
 
 	if ((vmx->nested.msrs.pinbased_ctls_high &