From 1976d2d2c91246a37fcb8246b811de735aa6e9a4 Mon Sep 17 00:00:00 2001 From: Takuya Yoshikawa Date: Fri, 5 Feb 2010 17:52:46 +0900 Subject: [PATCH] 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 Signed-off-by: Avi Kivity --- arch/x86/kvm/x86.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c91007f81660..bd3161c6daed 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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); -- 2.39.5