2017-07-11 15:50-0400, Bandan Das:
> Radim Krčmář <rkrcmar@xxxxxxxxxx> writes:
> > 2017-07-11 14:24-0400, Bandan Das:
> >> Bandan Das <bsd@xxxxxxxxxx> writes:
> >> > If there's a triple fault, I think it's a good idea to inject it
> >> > back. Basically, there's no need to take care of damage control
> >> > that L1 is intentionally doing.
> >> >
> >> >>> + goto fail;
> >> >>> + kvm_mmu_unload(vcpu);
> >> >>> + vmcs12->ept_pointer = address;
> >> >>> + kvm_mmu_reload(vcpu);
> >> >>
> >> >> I was thinking about something like this:
> >> >>
> >> >> kvm_mmu_unload(vcpu);
> >> >> old = vmcs12->ept_pointer;
> >> >> vmcs12->ept_pointer = address;
> >> >> if (kvm_mmu_reload(vcpu)) {
> >> >> /* pointer invalid, restore previous state */
> >> >> kvm_clear_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> >> >> vmcs12->ept_pointer = old;
> >> >> kvm_mmu_reload(vcpu);
> >> >> goto fail;
> >> >> }
> >> >>
> >> >> The you can inherit the checks from mmu_check_root().
> >>
> >> Actually, thinking about this a bit more, I agree with you. Any fault
> >> with a vmfunc operation should end with a vmfunc vmexit, so this
> >> is a good thing to have. Thank you for this idea! :)
> >
> > SDM says
> >
> > IF tent_EPTP is not a valid EPTP value (would cause VM entry to fail
> > if in EPTP) THEN VMexit;
>
> This section here:
> As noted in Section 25.5.5.2, an execution of the
> EPTP-switching VM function that causes a VM exit (as specified
> above), uses the basic exit reason 59, indicating “VMFUNC”.
> The length of the VMFUNC instruction is saved into the
> VM-exit instruction-length field. No additional VM-exit
> information is provided.
>
> Although, it adds (as specified above), from testing, any vmexit that
> happens as a result of the execution of the vmfunc instruction always
> has exit reason 59.
>
> IMO, the case David pointed out comes under "as a result of the
> execution of the vmfunc instruction", so I would prefer exiting
> with reason 59.
Right, the exit reason is 59 for reasons that trigger a VM exit
(i.e. invalid EPTP value, the four below), but kvm_mmu_reload() checks
unrelated stuff.
If the EPTP value is correct, then the switch should succeed.
If the EPTP is correct, but bogus, then the guest should get
EPT_MISCONFIG VM exit on its first access (when reading the
instruction). Source: I added
vmcs_write64(EPT_POINTER, vmcs_read64(EPT_POINTER) | (1ULL << 40));
shortly before a VMLAUNCH on L0. :)
I think that we might be emulating this case incorrectly and throwing
triple faults when it should be VM exits in vcpu_run().
> > and no other mentions of a VM exit, so I think that the VM exit happens
> > only under these conditions:
> >
> > — The EPT memory type (bits 2:0) must be a value supported by the
> > processor as indicated in the IA32_VMX_EPT_VPID_CAP MSR (see
> > Appendix A.10).
> > — Bits 5:3 (1 less than the EPT page-walk length) must be 3, indicating
> > an EPT page-walk length of 4; see Section 28.2.2.
> > — Bit 6 (enable bit for accessed and dirty flags for EPT) must be 0 if
> > bit 21 of the IA32_VMX_EPT_VPID_CAP MSR (see Appendix A.10) is read
> > as 0, indicating that the processor does not support accessed and
> > dirty flags for EPT.
> > — Reserved bits 11:7 and 63:N (where N is the processor’s
> > physical-address width) must all be 0.
> >
> > And it looks like we need parts of nested_ept_init_mmu_context() to
> > properly handle VMX_EPT_AD_ENABLE_BIT.
>
> I completely ignored AD and the #VE sections. I will add a TODO item
> in the comment section.
AFAIK, we don't support #VE, but AD would be nice to handle from the
beginning. (I think that caling nested_ept_init_mmu_context() as-is
isn't that bad.)
