Re: [PATCH 02/13] KVM: nVMX: Open a window for pending nested VMX preemption timer

[Jim Mattson]

On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> Add a kvm_x86_ops hook to detect a nested pending "hypervisor timer" and
> use it to effectively open a window for servicing the expired timer.
> Like pending SMIs on VMX, opening a window simply means requesting an
> immediate exit.
>
> This fixes a bug where an expired VMX preemption timer (for L2) will be
> delayed and/or lost if a pending exception is injected into L2.  The
> pending exception is rightly prioritized by vmx_check_nested_events()
> and injected into L2, with the preemption timer left pending.  Because
> no window opened, L2 is free to run uninterrupted.
>
> Fixes: f4124500c2c13 ("KVM: nVMX: Fully emulate preemption timer")
> Reported-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: Oliver Upton <oupton@xxxxxxxxxx>
> Cc: Peter Shier <pshier@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>