Even on a store, the optimization saves about 20 clock cycles (4-5%), mostly because the jump in write_memory_operand becomes much more predictable.
Signed-off-by: Paolo Bonzini <[email protected]> --- arch/x86/kvm/emulate.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 2c881e5cf5ad..541296f62b40 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1547,7 +1547,7 @@ exception: static int prepare_memory_operand(struct x86_emulate_ctxt *ctxt, struct operand *op, - bool write) + bool read, bool write) { int rc; unsigned long gva; @@ -1563,6 +1563,10 @@ static int prepare_memory_operand(struct x86_emulate_ctxt *ctxt, if (rc != X86EMUL_CONTINUE) return rc; + /* optimisation - avoid slow emulated read if Mov */ + if (!read) + return X86EMUL_CONTINUE; + if (likely(!kvm_is_error_hva(op->hva))) { rc = __copy_from_user(&op->val, (void __user *)op->hva, size); @@ -4643,14 +4647,14 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) } if ((ctxt->src.type == OP_MEM) && !(ctxt->d & NoAccess)) { - rc = prepare_memory_operand(ctxt, &ctxt->src, false); + rc = prepare_memory_operand(ctxt, &ctxt->src, true, false); if (rc != X86EMUL_CONTINUE) goto done; ctxt->src.orig_val64 = ctxt->src.val64; } if (ctxt->src2.type == OP_MEM) { - rc = prepare_memory_operand(ctxt, &ctxt->src2, false); + rc = prepare_memory_operand(ctxt, &ctxt->src2, true, false); if (rc != X86EMUL_CONTINUE) goto done; } @@ -4659,9 +4663,9 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) goto special_insn; - if ((ctxt->dst.type == OP_MEM) && !(ctxt->d & Mov)) { - /* optimisation - avoid slow emulated read if Mov */ + if (ctxt->dst.type == OP_MEM) { rc = prepare_memory_operand(ctxt, &ctxt->dst, + !(ctxt->d & Mov), !(ctxt->d & NoWrite)); if (rc != X86EMUL_CONTINUE) goto done; -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
