linux-kernel - [PATCH v3 2/4] KVM: VMX: Add a wrapper around ROL16() to get a vmcs12 from a field encoding

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Message-ID: <20260109041523.1027323-3-seanjc@google.com>
Date: Thu,  8 Jan 2026 20:15:21 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Chao Gao <chao.gao@...el.com>, Xin Li <xin@...or.com>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: [PATCH v3 2/4] 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 add 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@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/hyperv_evmcs.c | 2 +-
 arch/x86/kvm/vmx/hyperv_evmcs.h | 2 +-
 arch/x86/kvm/vmx/vmcs.h         | 1 +
 arch/x86/kvm/vmx/vmcs12.c       | 4 ++--
 arch/x86/kvm/vmx/vmcs12.h       | 2 +-
 5 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/hyperv_evmcs.c b/arch/x86/kvm/vmx/hyperv_evmcs.c
index 904bfcd1519b..cc728c9a3de5 100644
--- a/arch/x86/kvm/vmx/hyperv_evmcs.c
+++ b/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[] = {
diff --git a/arch/x86/kvm/vmx/hyperv_evmcs.h b/arch/x86/kvm/vmx/hyperv_evmcs.h
index 6536290f4274..fc7c4e7bd1bf 100644
--- a/arch/x86/kvm/vmx/hyperv_evmcs.h
+++ b/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;
diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h
index b25625314658..9aa204c87661 100644
--- a/arch/x86/kvm/vmx/vmcs.h
+++ b/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;
diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c
index 4233b5ca9461..c2ac9e1a50b3 100644
--- a/arch/x86/kvm/vmx/vmcs12.c
+++ b/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),
diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
index 4ad6b16525b9..7a5fdd9b27ba 100644
--- a/arch/x86/kvm/vmx/vmcs12.h
+++ b/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;
 
-- 
2.52.0.457.g6b5491de43-goog