2017-06-14 21:20 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: > 2017-06-14 21:02+0800, Wanpeng Li: >> 2017-06-14 20:52 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >> > 2017-06-14 09:07+0800, Wanpeng Li: >> >> 2017-06-14 2:55 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >> >> > Using vcpu->arch.cr2 is suspicious as VMX doesn't update CR2 on VM >> >> > exits; isn't this going to change the CR2 visible in L2 guest after a >> >> > nested VM entry? >> >> >> >> Sorry, I don't fully understand the question. As you know this >> >> vcpu->arch.cr2 which includes token is set before async pf injection, >> > >> > Yes, I'm thinking that setting vcpu->arch.cr2 is a mistake in this case. >> > >> >> and L1 will intercept it from EXIT_QUALIFICATION during nested vmexit, >> > >> > Right, so we do not need to have the token in CR2, because L1 is not >> > going to look at it. >> > >> >> why it can change the CR2 visible in L2 guest after a nested VM entry? >> > >> > Sorry, the situation is too convoluted to be expressed in one sentence: >> > >> > 1) L2 is running with CR2 = L2CR2 >> > 3) VMX exits (say, unrelated EXTERNAL_INTERRUPT) and L0 stores L2CR2 in >> > vcpu->arch.cr2 >> > 2) APF for L1 has completed >> > 4) L0 KVM wants to inject APF and sets vcpu->arch.cr2 = APFT >> > 5) L0 KVM does a nested VM exit to L1, EXIT_QUALIFICATION = APFT >> > 6) L0 KVM enters L1 with CR2 = vcpu->arch.cr2 = APFT >> > 7) L1 stores APFT as L2's CR2 >> > 8) L1 handles APF, maybe reschedules, but eventually comes back to this >> > L2's thread >> > 9) after some time, L1 enters L2 with CR2 = APFT >> > 10) L2 is running with CR2 = APTF >> > >> > The original L2CR2 is lost and we'd introduce a bug if L2 wanted to look >> > at it, e.g. it was in a process of handling its #PF. >> >> Good point. What's your proposal? :) > > Get rid of async_pf. :) Optimal solutions aside, I think it would be > best to add a new injection function for APF. One that injects a normal > #PF for non-nested guests and directly triggers a #PF VM exit otherwise, > and call it from kvm_arch_async_page_*present(). > > Do you think that just moving the nested VM exit from > nested_vmx_check_exception() would work? That's the same as what commit 9bc1f09f6fa76 (KVM: async_pf: avoid async pf injection when in guest mode) do I think, how about introducing a field like nested_apf_token to vcpu->arch to keep the token in kvm_inject_page_fault if (vcpu->arch.exception.async_page_fault && is_guest_mode(vcpu)) is true. Regards, Wanpeng Li
