KVM: selftests: Kill eptPageTablePointer

Replace the struct overlay with explicit bitmasks, which is clearer and
less error-prone. See commit f18b4ae ("kvm: selftests: do not use
bitfields larger than 32-bits for PTEs") for an example of why bitfields
are not preferable.

Remove the unused PAGE_SHIFT_4K definition while at it.

No functional change intended.

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251230230150.4150236-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: yosrym93

tools/testing/selftests/kvm/lib/x86/vmx.c

@@ -10,10 +10,16 @@
 #include "processor.h"
 #include "vmx.h"
 
-#define PAGE_SHIFT_4K  12
-
 #define KVM_EPT_PAGE_TABLE_MIN_PADDR 0x1c0000
 
+#define EPTP_MT_SHIFT		0 /* EPTP memtype bits 2:0 */
+#define EPTP_PWL_SHIFT		3 /* EPTP page walk length bits 5:3 */
+#define EPTP_AD_ENABLED_SHIFT	6 /* EPTP AD enabled bit 6 */
+
+#define EPTP_WB			(X86_MEMTYPE_WB << EPTP_MT_SHIFT)
+#define EPTP_PWL_4		(3ULL << EPTP_PWL_SHIFT) /* PWL is (levels - 1) */
+#define EPTP_AD_ENABLED		(1ULL << EPTP_AD_ENABLED_SHIFT)
+
 bool enable_evmcs;
 
 struct hv_enlightened_vmcs *current_evmcs;
@@ -34,14 +40,6 @@ struct eptPageTableEntry {
 	uint64_t suppress_ve:1;
 };
 
-struct eptPageTablePointer {
-	uint64_t memory_type:3;
-	uint64_t page_walk_length:3;
-	uint64_t ad_enabled:1;
-	uint64_t reserved_11_07:5;
-	uint64_t address:40;
-	uint64_t reserved_63_52:12;
-};
 int vcpu_enable_evmcs(struct kvm_vcpu *vcpu)
 {
 	uint16_t evmcs_ver;
@@ -196,16 +194,15 @@ static inline void init_vmcs_control_fields(struct vmx_pages *vmx)
 	vmwrite(PIN_BASED_VM_EXEC_CONTROL, rdmsr(MSR_IA32_VMX_TRUE_PINBASED_CTLS));
 
 	if (vmx->eptp_gpa) {
-		uint64_t ept_paddr;
-		struct eptPageTablePointer eptp = {
-			.memory_type = X86_MEMTYPE_WB,
-			.page_walk_length = 3, /* + 1 */
-			.ad_enabled = ept_vpid_cap_supported(VMX_EPT_VPID_CAP_AD_BITS),
-			.address = vmx->eptp_gpa >> PAGE_SHIFT_4K,
-		};
-
-		memcpy(&ept_paddr, &eptp, sizeof(ept_paddr));
-		vmwrite(EPT_POINTER, ept_paddr);
+		uint64_t eptp = vmx->eptp_gpa | EPTP_WB | EPTP_PWL_4;
+
+		TEST_ASSERT((vmx->eptp_gpa & ~PHYSICAL_PAGE_MASK) == 0,
+			    "Illegal bits set in vmx->eptp_gpa");
+
+		if (ept_vpid_cap_supported(VMX_EPT_VPID_CAP_AD_BITS))
+			eptp |= EPTP_AD_ENABLED;
+
+		vmwrite(EPT_POINTER, eptp);
 		sec_exec_ctl |= SECONDARY_EXEC_ENABLE_EPT;
 	}