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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>
hifive-unleashed-5.1
Takuya Yoshikawa 2010-02-05 17:52:46 +09:00 committed by Marcelo Tosatti
parent 6316e1c8c6
commit 1976d2d2c9
1 changed files with 4 additions and 2 deletions
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6
arch/x86/kvm/x86.c
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@ -3551,8 +3551,10 @@ int kvm_emulate_pio(struct kvm_vcpu *vcpu, int in, int size, unsigned port)
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);