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    SubjectRE: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set
    Date


    > -----Original Message-----
    > From: iommu-bounces@lists.linux-foundation.org
    > [mailto:iommu-bounces@lists.linux-foundation.org] On Behalf Of Zhang, Yang Z
    > Sent: Thursday, December 18, 2014 11:10 PM
    > To: Paolo Bonzini; kvm@vger.kernel.org
    > Cc: iommu@lists.linux-foundation.org; linux-kernel@vger.kernel.org;
    > kvm@vger.kernel.org
    > Subject: RE: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is set
    >
    > Paolo Bonzini wrote on 2014-12-18:
    > >
    > >
    > > On 18/12/2014 04:14, Wu, Feng wrote:
    > >>
    > >>
    > >> linux-kernel-owner@vger.kernel.org wrote on
    > mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Paolo:
    > >>> x86@kernel.org; Gleb Natapov; Paolo Bonzini; dwmw2@infradead.org;
    > >>> joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org; Alex Williamson;
    > >>> joro-zLv9SwRftAIdnm+Jiang
    > >>> Liu
    > >>> Cc: iommu@lists.linux-foundation.org;
    > >>> linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; KVM list;
    > >>> Eric Auger
    > >>> Subject: Re: [v3 25/26] KVM: Suppress posted-interrupt when 'SN' is
    > >>> set
    > >>>
    > >>>
    > >>>
    > >>> On 12/12/2014 16:14, Feng Wu wrote:
    > >>>> Currently, we don't support urgent interrupt, all interrupts are
    > >>>> recognized as non-urgent interrupt, so we cannot send
    > >>>> posted-interrupt when 'SN' is set.
    > >>>
    > >>> Can this happen? If the vcpu is in guest mode, it cannot have been
    > >>> scheduled out, and that's the only case when SN is set.
    > >>>
    > >>> Paolo
    > >>
    > >> Currently, the only place where SN is set is vCPU is preempted and
    >
    > If the vCPU is preempted, shouldn't the subsequent be ignored? What happens
    > if a PI is occurs when vCPU is preempted?

    If a vCPU is preempted, the 'SN' bit is set, the subsequent interrupts are
    suppressed for posting.

    Thanks,
    Feng

    >
    > >> waiting for the next scheduling in the runqueue. But I am not sure
    > >> whether we need to set SN for other purpose in future. Adding SN
    > >> checking here is just to follow the Spec. non-urgent interrupts are
    > >> suppressed
    > > when SN is set.
    > >
    > > I would change that to a WARN_ON_ONCE then.
    >
    >
    > Best regards,
    > Yang
    >
    >
    > _______________________________________________
    > iommu mailing list
    > iommu@lists.linux-foundation.org
    > https://lists.linuxfoundation.org/mailman/listinfo/iommu


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