KVM: Remove redundant reading of rax on OUT instructions
kvm_emulate_pio() and complete_pio() both read out the
RAX register value and copy it to a place into which
the value read out from the port will be copied later.
This patch removes this redundancy.
/*** snippet from arch/x86/kvm/x86.c ***/
int complete_pio(struct kvm_vcpu *vcpu)
{
...
if (!io->string) {
if (io->in) {
val = kvm_register_read(vcpu, VCPU_REGS_RAX);
memcpy(&val, vcpu->arch.pio_data, io->size);
kvm_register_write(vcpu, VCPU_REGS_RAX, val);
}
...
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c91007f..bd3161c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3551,8 +3551,10 @@
trace_kvm_pio(vcpu->run->io.direction == KVM_EXIT_IO_OUT, port,
size, 1);
- val = kvm_register_read(vcpu, VCPU_REGS_RAX);
- memcpy(vcpu->arch.pio_data, &val, 4);
+ if (!vcpu->arch.pio.in) {
+ val = kvm_register_read(vcpu, VCPU_REGS_RAX);
+ memcpy(vcpu->arch.pio_data, &val, 4);
+ }
if (!kernel_pio(vcpu, vcpu->arch.pio_data)) {
complete_pio(vcpu);