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? :) Regards, Wanpeng Li
