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

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Date:   Thu, 16 Jun 2022 16:47:10 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH v2 01/21] KVM: nVMX: Unconditionally purge queued/injected
 events on nested "exit"

On Tue, Jun 14, 2022 at 1:47 PM Sean Christopherson <seanjc@...gle.com> 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@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>