On February 21, 2017 11:07 AM, Tian, Kevin wrote: >> From: Xuquan (Quan Xu) [mailto:xuqu...@huawei.com] >> Sent: Tuesday, February 21, 2017 10:49 AM >> >> On February 20, 2017 4:24 PM, Chao Gao wrote: >> >On Mon, Feb 20, 2017 at 11:25:29AM +0000, Xuquan (Quan Xu) wrote: >> >>On February 18, 2017 12:33 AM, Jan Beulich wrote: >> >>>>>> On 17.02.17 at 09:49, <chao....@intel.com> wrote: >> >>>> On Fri, Feb 17, 2017 at 09:37:45AM +0000, Xuquan (Quan Xu) wrote: >> >>>>>From a589074281cc22a30ed75a5bccba60e83d2312a6 Mon Sep 17 >> >>>00:00:00 2001 >> >>>>>From: Quan Xu <xuqu...@huawei.com> >> >>>>>Date: Sat, 18 Feb 2017 09:27:37 +0800 >> >>>>>Subject: [PATCH] x86/apicv: enhance posted-interrupt processing >> >>>>> >> >>>>>If guest is already in non-root mode, an posted interrupt will be >> >>>>>directly delivered to guest (leaving softirq being set w/o >> >>>>>actually incurring a VM-Exit - breaking desired softirq behavior). >> >>>>>Then further posted interrupts will skip the IPI, stay in PIR and >> >>>>>not noted until another VM-Exit happens. >> >>>>> >> >>>>>Remove the softirq set. Actually since it's an optimization for >> >>>>>less IPIs, check softirq_pending(cpu) directly instead of >> >>>>>sticking to one bit only. >> >>>>> >> >>>>>Signed-off-by: Quan Xu <xuqu...@huawei.com> >> >>>>>--- >> >>>>> xen/arch/x86/hvm/vmx/vmx.c | 3 +-- >> >>>>> 1 file changed, 1 insertion(+), 2 deletions(-) >> >>>>> >> >>>>>diff --git a/xen/arch/x86/hvm/vmx/vmx.c >> >b/xen/arch/x86/hvm/vmx/vmx.c >> >>>>>index 61925cf..3887c32 100644 >> >>>>>--- a/xen/arch/x86/hvm/vmx/vmx.c >> >>>>>+++ b/xen/arch/x86/hvm/vmx/vmx.c >> >>>>>@@ -1846,8 +1846,7 @@ static void >> >>>__vmx_deliver_posted_interrupt(struct vcpu *v) >> >>>>> { >> >>>>> unsigned int cpu = v->processor; >> >>>>> >> >>>>>- if ( !test_and_set_bit(VCPU_KICK_SOFTIRQ, >> >>>&softirq_pending(cpu)) >> >>>>>- && (cpu != smp_processor_id()) ) >> >>>>>+ if ( !softirq_pending(cpu) && (cpu != >> >>>>>+ smp_processor_id()) ) >> >>>> HI, Quan. >> >>>> Is there a situation that we need set VCPU_KICK_SOFTIRQ. For >> >>>> example, after vmx_intr_assist(), a interrupt happened and its >> >>>> handler called this function to deliver interrupt to current vcpu. >> >>>> In that case, the interrupt would not be injected to guest before >> >>>> this VM-entry for we don't generate a softirq and don't send a >> >>>> self-IPI >> >to current vcpu. >> >>> >> >> >> >>Chao, __iiuc__, your question may be from the comments of >> >xen/arch/x86/hvm/vmx/vmx.c :: pi_notification_interrupt() .. >> >>IF VT-d PI is enabled, >> >> VCPU_KICK_SOFTIRQ bit is set by ' >> >>raise_softirq(VCPU_KICK_SOFTIRQ)', >> >at the end of pi_notification_interrupt().. >> >>Else >> >> Is it possible for your case? >> >> >> >If vcpu is in root mode and is to do VM-entry, it has synced PIR to vIRR. >> >Now a interrupt (e.g. PMU_APIC_VECTOR) happens. Thus it goes >> >following the path >> >pmu_apic_interrupt->vpmu_do_interrupt->vlapic_set_irq(assume >> >it will inject a interrupt to current vcpu) >> >-> vmx_deliver_posted_intr( set one bit in PIR )-> >> >-> __vmx_deliver_posted_interrupt >> >Assuming that there is no softirq pending, the code after change >> >doesn't generate a IPI for (cpu == smp_processor_id()). In this case, >> >this interrupt would not be injected to guest before this VM-entry. >> >Although there are many assumption in the explaination, I think it >> >may be possible. >> > >> >> So far, I agree to add VCPU_KICK_SOFTIRQ bit in a nice way.. >> Even we have checked whether the vCPU is running or not at the >> beginning of __vmx_deliver_posted_interrupt(), we can't grantee the >> vcpu is still in guest mode at the point to call this IPI.. >> as in an extreme case, at the point to call this IPI, all of vCPUs are >> in root-mode, the posted-interrupt won't be delivered.. > >I don't understand of your concern of whether guest is in guest mode here.
If the vCPUs are in root-mode, whatever we do we can't deliver posted interrupt Successfully. ... >The purpose of this function is not to guarantee posted-interrupt is always >used (cannot unless you pause remote cpu). It's just a best effort. ... the best effort, you mentioned here, __iiuc__, we will sync PIRR to vIRR before vmentry.. if we don't set VCPU_KICK_SOFTIRQ bit, the pending interrupt in PIRR will be not synced to vIRR before vm-entry in time. In an extreme case, if there is only one interrupt pending interrupt in PIRR (no other caller to set VCPU_KICK_SOFTIRQ bit), The pending interrupt in PIRR will never be delivered to guest later.. ... > If target >vcpu is in root mode, then this IPI causes a real interrupt on remote cpu as >notification (then the handler pi_notification_interrupt you copied earlier >will jump in to help). > > ... The posted_intr_vector handler is not always pi_notification_interrupt. If the vt-d PI is not enabled, the handler is event_check_interrupt.. The VCPU_KICK_SOFTIRQ bit is set in pi_notification_interrupt , but not event_check_interrupt.. -I'd be very sorry if my description is still not clear.. Quan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
