KVM: VMX: Add a wrapper around ROL16() to get a vmcs12 from a field encoding

Add a wrapper macro, ENC_TO_VMCS12_IDX(), to get a vmcs12 index given a
field encoding in anticipation of adding a macro to get from a vmcs12 index
back to the field encoding.  And because open coding ROL16(n, 6) everywhere
is gross.

No functional change intended.

Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://patch.msgid.link/20260115173427.716021-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/vmx/hyperv_evmcs.c

@@ -7,7 +7,7 @@
 #include "hyperv_evmcs.h"
 
 #define EVMCS1_OFFSET(x) offsetof(struct hv_enlightened_vmcs, x)
-#define EVMCS1_FIELD(number, name, clean_field)[ROL16(number, 6)] = \
+#define EVMCS1_FIELD(number, name, clean_field)[ENC_TO_VMCS12_IDX(number)] = \
 		{EVMCS1_OFFSET(name), clean_field}
 
 const struct evmcs_field vmcs_field_to_evmcs_1[] = {

arch/x86/kvm/vmx/hyperv_evmcs.h

@@ -130,7 +130,7 @@ static __always_inline int evmcs_field_offset(unsigned long field,
 					      u16 *clean_field)
 {
 	const struct evmcs_field *evmcs_field;
-	unsigned int index = ROL16(field, 6);
+	unsigned int index = ENC_TO_VMCS12_IDX(field);
 
 	if (unlikely(index >= nr_evmcs_1_fields))
 		return -ENOENT;

arch/x86/kvm/vmx/vmcs.h

@@ -12,6 +12,7 @@
 #include "capabilities.h"
 
 #define ROL16(val, n) ((u16)(((u16)(val) << (n)) | ((u16)(val) >> (16 - (n)))))
+#define ENC_TO_VMCS12_IDX(enc) ROL16(enc, 6)
 
 struct vmcs_hdr {
 	u32 revision_id:31;

arch/x86/kvm/vmx/vmcs12.c

@@ -4,10 +4,10 @@
 #include "vmcs12.h"
 
 #define VMCS12_OFFSET(x) offsetof(struct vmcs12, x)
-#define FIELD(number, name)	[ROL16(number, 6)] = VMCS12_OFFSET(name)
+#define FIELD(number, name)	[ENC_TO_VMCS12_IDX(number)] = VMCS12_OFFSET(name)
 #define FIELD64(number, name)						\
 	FIELD(number, name),						\
-	[ROL16(number##_HIGH, 6)] = VMCS12_OFFSET(name) + sizeof(u32)
+	[ENC_TO_VMCS12_IDX(number##_HIGH)] = VMCS12_OFFSET(name) + sizeof(u32)
 
 const unsigned short vmcs12_field_offsets[] = {
 	FIELD(VIRTUAL_PROCESSOR_ID, virtual_processor_id),

arch/x86/kvm/vmx/vmcs12.h

@@ -385,7 +385,7 @@ static inline short get_vmcs12_field_offset(unsigned long field)
 	if (field >> 15)
 		return -ENOENT;
 
-	index = ROL16(field, 6);
+	index = ENC_TO_VMCS12_IDX(field);
 	if (index >= nr_vmcs12_fields)
 		return -ENOENT;