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Date: Wed, 19 Jan 2022 15:12:09 +0800 From: Wanpeng Li <kernellwp@...il.com> To: Paolo Bonzini <pbonzini@...hat.com> Cc: LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>, Sean Christopherson <seanjc@...gle.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, Aili Yao <yaoaili@...gsoft.com> Subject: Re: [PATCH v2] KVM: LAPIC: Enable timer posted-interrupt when mwait/hlt is advertised kindly ping, :) On Thu, 6 Jan 2022 at 20:21, Wanpeng Li <kernellwp@...il.com> wrote: > > From: Wanpeng Li <wanpengli@...cent.com> > > As commit 0c5f81dad46 (KVM: LAPIC: Inject timer interrupt via posted interrupt) > mentioned that the host admin should well tune the guest setup, so that vCPUs > are placed on isolated pCPUs, and with several pCPUs surplus for *busy* housekeeping. > It is better to disable mwait/hlt/pause vmexits to keep the vCPUs in non-root > mode. However, we may isolate pCPUs for other purpose like DPDK or we can make > some guests isolated and others not, we may lose vmx preemption timer/timer fastpath > due to not well tuned setup, and the checking in kvm_can_post_timer_interrupt() > is not enough. Let's guarantee mwait/hlt is advertised before enabling posted-interrupt > interrupt. vmx preemption timer/timer fastpath can continue to work if both of them > are not advertised. > > Reported-by: Aili Yao <yaoaili@...gsoft.com> > Cc: Aili Yao <yaoaili@...gsoft.com> > Cc: Sean Christopherson <seanjc@...gle.com> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com> > --- > v1 -> v2: > * also check kvm_hlt_in_guest since sometime mwait is disabled on host > > arch/x86/kvm/lapic.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index f206fc3..fdb7c81 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -113,7 +113,8 @@ static inline u32 kvm_x2apic_id(struct kvm_lapic *apic) > > static bool kvm_can_post_timer_interrupt(struct kvm_vcpu *vcpu) > { > - return pi_inject_timer && kvm_vcpu_apicv_active(vcpu); > + return pi_inject_timer && kvm_vcpu_apicv_active(vcpu) && > + (kvm_mwait_in_guest(vcpu->kvm) || kvm_hlt_in_guest(vcpu->kvm)); > } > > bool kvm_can_use_hv_timer(struct kvm_vcpu *vcpu) > -- > 2.7.4 >
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