KVM: emulate: speed up emulated moves

We can just blindly move all 16 bytes of ctxt->src's value to ctxt->dst.
write_register_operand will take care of writing only the lower bytes.

Avoiding a call to memcpy (the compiler optimizes it out) gains about
200 cycles on kvm-unit-tests for register-to-register moves, and makes
them about as fast as arithmetic instructions.

We could perhaps get a larger speedup by moving all instructions _except_
moves out of x86_emulate_insn, removing opcode_len, and replacing the
switch statement with an inlined em_mov.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 0e0151c..4324473 100644 (file)
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -233,7 +233,7 @@ struct operand {
        union {
                unsigned long val;
                u64 val64;
-               char valptr[sizeof(unsigned long) + 2];
+               char valptr[sizeof(sse128_t)];
                sse128_t vec_val;
                u64 mm_val;
                void *data;

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index ea56dae..27f677e 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2990,7 +2990,7 @@ static int em_rdpmc(struct x86_emulate_ctxt *ctxt)
 
 static int em_mov(struct x86_emulate_ctxt *ctxt)
 {
-       memcpy(ctxt->dst.valptr, ctxt->src.valptr, ctxt->op_bytes);
+       memcpy(ctxt->dst.valptr, ctxt->src.valptr, sizeof(ctxt->src.valptr));
        return X86EMUL_CONTINUE;
 }