Skip the VMWRITE to update GUEST_CR3 if CR3 is not available, i.e. has not been read from the VMCS since the last VM-Enter. If vcpu->arch.cr3 is stale, kvm_read_cr3(vcpu) will refresh vcpu->arch.cr3 from the VMCS, meaning KVM will do a VMREAD and then VMWRITE the value it just pulled from the VMCS. Note, this is a purely theoretical change, no instances of skipping the VMREAD+VMWRITE have been observed with this change. Tested-by: Reto Buerki <reet@xxxxxxxxxxx> Tested-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> --- arch/x86/kvm/vmx/vmx.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 7679c2a05a50..0b8dd9c315f8 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -3004,10 +3004,12 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) /* Loading vmcs02.GUEST_CR3 is handled by nested VM-Enter. */ if (is_guest_mode(vcpu)) update_guest_cr3 = false; - else if (enable_unrestricted_guest || is_paging(vcpu)) - guest_cr3 = kvm_read_cr3(vcpu); - else + else if (!enable_unrestricted_guest && !is_paging(vcpu)) guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr; + else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail)) + guest_cr3 = vcpu->arch.cr3; + else /* vmcs01.GUEST_CR3 is already up-to-date. */ + update_guest_cr3 = false; ept_load_pdptrs(vcpu); } -- 2.22.0
