From d3edefc0035669e8817d1d5c32ef03e882477323 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Tue, 16 Jun 2009 12:33:56 +0300 Subject: [PATCH] KVM: VMX: Only reload guest cr2 if different from host cr2 cr2 changes only rarely, and writing it is expensive. Avoid the costly cr2 writes by checking if it does not already hold the desired value. Shaves 70 cycles off the vmexit latency. Signed-off-by: Avi Kivity --- arch/x86/kvm/vmx.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index fc8d49c..1a84ca1 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3651,11 +3651,16 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) "mov %%"R"sp, %c[host_rsp](%0) \n\t" __ex(ASM_VMX_VMWRITE_RSP_RDX) "\n\t" "1: \n\t" + /* Reload cr2 if changed */ + "mov %c[cr2](%0), %%"R"ax \n\t" + "mov %%cr2, %%"R"dx \n\t" + "cmp %%"R"ax, %%"R"dx \n\t" + "je 2f \n\t" + "mov %%"R"ax, %%cr2 \n\t" + "2: \n\t" /* Check if vmlaunch of vmresume is needed */ "cmpl $0, %c[launched](%0) \n\t" /* Load guest registers. Don't clobber flags. */ - "mov %c[cr2](%0), %%"R"ax \n\t" - "mov %%"R"ax, %%cr2 \n\t" "mov %c[rax](%0), %%"R"ax \n\t" "mov %c[rbx](%0), %%"R"bx \n\t" "mov %c[rdx](%0), %%"R"dx \n\t" -- 2.7.4