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authorAvi Kivity <avi@redhat.com>2009-06-16 12:33:56 +0300
committerAvi Kivity <avi@redhat.com>2009-09-10 08:32:57 +0300
commitd3edefc0035669e8817d1d5c32ef03e882477323 (patch)
tree7fde2dfa8f43e1619e0d31549e54fef4d19a374d /arch
parent681405bfc73a2717ae9b03b2bad465b009106f31 (diff)
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@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/vmx.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fc8d49c6bc5..1a84ca191cd 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"