[PATCH 02/10] KVM: emulate: move Src2Shift up one bit

Paolo Bonzini
2025-11-14T00:36:41Z

An irresistible microoptimization (changing accesses to Src2 to just an
AND :)) that also frees a bit for AVX in the low flags word. This makes
it closer to SSE since both of them can access XMM registers, pointlessly
shaving another clock cycle or two (maybe).

No functional change intended.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/emulate.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 43ae4fcb2137..57799b5d9da2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -147,7 +147,7 @@
#define PageTable (1 << 29) /* instruction used to write page table */
#define NotImpl (1 << 30) /* instruction is not implemented */
/* Source 2 operand type */
-#define Src2Shift (31)
+#define Src2Shift (32) /* bits 32-36 */
#define Src2None (OpNone << Src2Shift)
#define Src2Mem (OpMem << Src2Shift)
#define Src2CL (OpCL << Src2Shift)
@@ -161,6 +161,7 @@
#define Src2FS (OpFS << Src2Shift)
#define Src2GS (OpGS << Src2Shift)
#define Src2Mask (OpMask << Src2Shift)
+/* free: 37-39 */
#define Mmx ((u64)1 << 40) /* MMX Vector instruction */
#define AlignMask ((u64)7 << 41)
#define Aligned ((u64)1 << 41) /* Explicitly aligned (e.g. MOVDQA) */
--
2.43.5