Re: [PATCH v2 01/21] KVM: nVMX: Unconditionally purge queued/injected events on nested "exit"

[Jim Mattson]

On Tue, Jun 14, 2022 at 1:47 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Drop pending exceptions and events queued for re-injection when leaving
> nested guest mode, even if the "exit" is due to VM-Fail, SMI, or forced
> by host userspace.  Failure to purge events could result in an event
> belonging to L2 being injected into L1.
>
> This _should_ never happen for VM-Fail as all events should be blocked by
> nested_run_pending, but it's possible if KVM, not the L1 hypervisor, is
> the source of VM-Fail when running vmcs02.
>
> SMI is a nop (barring unknown bugs) as recognition of SMI and thus entry
> to SMM is blocked by pending exceptions and re-injected events.
>
> Forced exit is definitely buggy, but has likely gone unnoticed because
> userspace probably follows the forced exit with KVM_SET_VCPU_EVENTS (or
> some other ioctl() that purges the queue).
>
> Fixes: 4f350c6dbcb9 ("kvm: nVMX: Handle deferred early VMLAUNCH/VMRESUME failure properly")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>