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Date: Wed, 19 Aug 2009 16:02:14 +0300 From: Avi Kivity <avi@...hat.com> To: kvm@...r.kernel.org Cc: linux-kernel@...r.kernel.org Subject: [PATCH 18/47] 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 <avi@...hat.com> --- arch/x86/kvm/vmx.c | 9 +++++++-- 1 files 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" -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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