Re: [PATCH-for-4.13 2/2] KVM: VMX: remove WARN_ON_ONCE in kvm_vcpu_trigger_posted_interrupt

[Greg KH <greg@kroah.com>]

On Wed, Sep 27, 2017 at 11:22:40AM +0800, Haozhong Zhang wrote:
> commit 5753743fa5108b8f98bd61e40dc63f641b26c768 upstream.
> 
> WARN_ON_ONCE(pi_test_sn(&vmx->pi_desc)) in kvm_vcpu_trigger_posted_interrupt()
> intends to detect the violation of invariant that VT-d PI notification
> event is not suppressed when vcpu is in the guest mode. Because the
> two checks for the target vcpu mode and the target suppress field
> cannot be performed atomically, the target vcpu mode may change in
> between. If that does happen, WARN_ON_ONCE() here may raise false
> alarms.
> 
> As the previous patch fixed the real invariant breaker, remove this
> WARN_ON_ONCE() to avoid false alarms, and document the allowed cases
> instead.
> 
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> Reported-by: "Ramamurthy, Venkatesh" <venkatesh.ramamurthy@intel.com>
> Reported-by: Dan Williams <dan.j.williams@intel.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Fixes: 28b835d60fcc ("KVM: Update Posted-Interrupts Descriptor when vCPU is preempted")

Also applied to 4.4 and 4.9-stable trees, thanks.

greg k-h