KVM: nVMX: Track vmcs12 offsets for shadowed VMCS fields

The vmcs12 fields offsets are constant and known at compile time.  Store
the associated offset for each shadowed field to avoid the costly lookup
in vmcs_field_to_offset() when copying between vmcs12 and the shadow
VMCS.  Avoiding the costly lookup reduces the latency of copying by
~100 cycles in each direction.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 18 insertions, 39 deletions

diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
index 3a742428ad17..9cd26099fcc0 100644
--- a/arch/x86/kvm/vmx/vmcs12.h
+++ b/arch/x86/kvm/vmx/vmcs12.h
@@ -394,69 +394,48 @@ static inline short vmcs_field_to_offset(unsigned long field)
 
 #undef ROL16
 
-/*
- * Read a vmcs12 field. Since these can have varying lengths and we return
- * one type, we chose the biggest type (u64) and zero-extend the return value
- * to that size. Note that the caller, handle_vmread, might need to use only
- * some of the bits we return here (e.g., on 32-bit guests, only 32 bits of
- * 64-bit fields are to be returned).
- */
-static inline int vmcs12_read_any(struct vmcs12 *vmcs12,
-				  unsigned long field, u64 *ret)
+static inline u64 vmcs12_read_any(struct vmcs12 *vmcs12, unsigned long field,
+				  u16 offset)
 {
-	short offset = vmcs_field_to_offset(field);
-	char *p;
-
-	if (offset < 0)
-		return offset;
-
-	p = (char *)vmcs12 + offset;
+	char *p = (char *)vmcs12 + offset;
 
 	switch (vmcs_field_width(field)) {
 	case VMCS_FIELD_WIDTH_NATURAL_WIDTH:
-		*ret = *((natural_width *)p);
-		return 0;
+		return *((natural_width *)p);
 	case VMCS_FIELD_WIDTH_U16:
-		*ret = *((u16 *)p);
-		return 0;
+		return *((u16 *)p);
 	case VMCS_FIELD_WIDTH_U32:
-		*ret = *((u32 *)p);
-		return 0;
+		return *((u32 *)p);
 	case VMCS_FIELD_WIDTH_U64:
-		*ret = *((u64 *)p);
-		return 0;
+		return *((u64 *)p);
 	default:
-		WARN_ON(1);
-		return -ENOENT;
+		WARN_ON_ONCE(1);
+		return -1;
 	}
 }
 
-static inline int vmcs12_write_any(struct vmcs12 *vmcs12,
-				   unsigned long field, u64 field_value){
-	short offset = vmcs_field_to_offset(field);
+static inline void vmcs12_write_any(struct vmcs12 *vmcs12, unsigned long field,
+				    u16 offset, u64 field_value)
+{
 	char *p = (char *)vmcs12 + offset;
 
-	if (offset < 0)
-		return offset;
-
 	switch (vmcs_field_width(field)) {
 	case VMCS_FIELD_WIDTH_U16:
 		*(u16 *)p = field_value;
-		return 0;
+		break;
 	case VMCS_FIELD_WIDTH_U32:
 		*(u32 *)p = field_value;
-		return 0;
+		break;
 	case VMCS_FIELD_WIDTH_U64:
 		*(u64 *)p = field_value;
-		return 0;
+		break;
 	case VMCS_FIELD_WIDTH_NATURAL_WIDTH:
 		*(natural_width *)p = field_value;
-		return 0;
+		break;
 	default:
-		WARN_ON(1);
-		return -ENOENT;
+		WARN_ON_ONCE(1);
+		break;
 	}
-
 }
 
 #endif /* __KVM_X86_VMX_VMCS12_H */