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

Use macros in vmx_restore_vmx_basic() 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: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20240605231918.2915961-7-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/vmx/nested.c

@@ -1251,21 +1251,32 @@ static bool is_bitwise_subset(u64 superset, u64 subset, u64 mask)
 
 static int vmx_restore_vmx_basic(struct vcpu_vmx *vmx, u64 data)
 {
-	const u64 feature_and_reserved =
-		/* feature (except bit 48; see below) */
-		BIT_ULL(49) | BIT_ULL(54) | BIT_ULL(55) |
-		/* reserved */
-		BIT_ULL(31) | GENMASK_ULL(47, 45) | GENMASK_ULL(63, 56);
+	const u64 feature_bits = VMX_BASIC_DUAL_MONITOR_TREATMENT |
+				 VMX_BASIC_INOUT |
+				 VMX_BASIC_TRUE_CTLS;
+
+	const u64 reserved_bits = GENMASK_ULL(63, 56) |
+				  GENMASK_ULL(47, 45) |
+				  BIT_ULL(31);
+
 	u64 vmx_basic = vmcs_config.nested.basic;
 
-	if (!is_bitwise_subset(vmx_basic, data, feature_and_reserved))
+	BUILD_BUG_ON(feature_bits & reserved_bits);
+
+	/*
+	 * Except for 32BIT_PHYS_ADDR_ONLY, which is an anti-feature bit (has
+	 * inverted polarity), 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_basic, data, feature_bits | reserved_bits))
 		return -EINVAL;
 
 	/*
 	 * KVM does not emulate a version of VMX that constrains physical
 	 * addresses of VMX structures (e.g. VMCS) to 32-bits.
 	 */
-	if (data & BIT_ULL(48))
+	if (data & VMX_BASIC_32BIT_PHYS_ADDR_ONLY)
 		return -EINVAL;
 
 	if (vmx_basic_vmcs_revision_id(vmx_basic) !=