On Wed, Oct 14, 2015 at 6:33 PM, Wu, Feng <feng.wu@xxxxxxxxx> wrote: > >> -----Original Message----- >> From: David Matlack [mailto:dmatlack@xxxxxxxxxx] >> Sent: Thursday, October 15, 2015 7:41 AM >> To: Wu, Feng <feng.wu@xxxxxxxxx> >> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>; alex.williamson@xxxxxxxxxx; Joerg >> Roedel <joro@xxxxxxxxxx>; Marcelo Tosatti <mtosatti@xxxxxxxxxx>; >> eric.auger@xxxxxxxxxx; kvm list <kvm@xxxxxxxxxxxxxxx>; iommu@lists.linux- >> foundation.org; linux-kernel@xxxxxxxxxxxxxxx >> Subject: Re: [PATCH v9 17/18] KVM: Update Posted-Interrupts Descriptor when >> vCPU is blocked >> >> Hi Feng. >> >> On Fri, Sep 18, 2015 at 7:29 AM, Feng Wu <feng.wu@xxxxxxxxx> wrote: >> > This patch updates the Posted-Interrupts Descriptor when vCPU >> > is blocked. >> > >> > pre-block: >> > - Add the vCPU to the blocked per-CPU list >> > - Set 'NV' to POSTED_INTR_WAKEUP_VECTOR >> > >> > post-block: >> > - Remove the vCPU from the per-CPU list >> >> I'm wondering what happens if a posted interrupt arrives at the IOMMU >> after pre-block and before post-block. >> >> In pre_block, NV is set to POSTED_INTR_WAKEUP_VECTOR. IIUC, this means >> future posted interrupts will not trigger "Posted-Interrupt Processing" >> (PIR will not get copied to VIRR). Instead, the IOMMU will do ON := 1, >> PIR |= (1 << vector), and send POSTED_INTR_WAKEUP_VECTOR. PIWV calls >> wakeup_handler which does kvm_vcpu_kick. kvm_vcpu_kick does a wait-queue >> wakeup and possibly a scheduler ipi. >> >> But the VCPU is sitting in kvm_vcpu_block. It spins and/or schedules >> (wait queue) until it has a reason to wake up. I couldn't find a code >> path from kvm_vcpu_block that lead to checking ON or PIR. How does the >> blocked VCPU "receive" the posted interrupt? (And when does Posted- >> Interrupt Processing get triggered?) > > In the pre_block, it also change the 'NDST' filed to the pCPU, on which the vCPU > is put to the per-CPU list 'blocked_vcpu_on_cpu', so when posted-interrupts > come it, it will sent the wakeup notification event to the pCPU above, then in > the wakeup_handler, it can find the vCPU from the per-CPU list, hence > kvm_vcpu_kick can wake up it. Thank you for your response. I was actually confused about something else. After wakeup_handler->kvm_vcpu_kick causes the vcpu to wake up, that vcpu calls kvm_vcpu_check_block() to check if there are pending events, otherwise the vcpu goes back to sleep. I had trouble yesterday finding the code path from kvm_vcpu_check_block() which checks PIR/ON. But after spending more time reading the source code this morning I found that kvm_vcpu_check_block() eventually calls into vmx_sync_pir_to_irr(), which copies PIR to IRR and clears ON. And then apic_find_highest_irr() detects the pending posted interrupt. > > Thanks, > Feng > >> >> Thanks! >> >> > >> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx> >> > --- >> > v9: >> > - Add description for blocked_vcpu_on_cpu_lock in >> Documentation/virtual/kvm/locking.txt >> > - Check !kvm_arch_has_assigned_device(vcpu->kvm) first, then >> > !irq_remapping_cap(IRQ_POSTING_CAP) >> > >> > v8: >> > - Rename 'pi_pre_block' to 'pre_block' >> > - Rename 'pi_post_block' to 'post_block' >> > - Change some comments >> > - Only add the vCPU to the blocking list when the VM has assigned devices. >> > >> > Documentation/virtual/kvm/locking.txt | 12 +++ >> > arch/x86/include/asm/kvm_host.h | 13 +++ >> > arch/x86/kvm/vmx.c | 153 >> ++++++++++++++++++++++++++++++++++ >> > arch/x86/kvm/x86.c | 53 +++++++++--- >> > include/linux/kvm_host.h | 3 + >> > virt/kvm/kvm_main.c | 3 + >> > 6 files changed, 227 insertions(+), 10 deletions(-) >> > >> > diff --git a/Documentation/virtual/kvm/locking.txt >> b/Documentation/virtual/kvm/locking.txt >> > index d68af4d..19f94a6 100644 >> > --- a/Documentation/virtual/kvm/locking.txt >> > +++ b/Documentation/virtual/kvm/locking.txt >> > @@ -166,3 +166,15 @@ Comment: The srcu read lock must be held while >> accessing memslots (e.g. >> > MMIO/PIO address->device structure mapping (kvm->buses). >> > The srcu index can be stored in kvm_vcpu->srcu_idx per vcpu >> > if it is needed by multiple functions. >> > + >> > +Name: blocked_vcpu_on_cpu_lock >> > +Type: spinlock_t >> > +Arch: x86 >> > +Protects: blocked_vcpu_on_cpu >> > +Comment: This is a per-CPU lock and it is used for VT-d posted-interrupts. >> > + When VT-d posted-interrupts is supported and the VM has assigned >> > + devices, we put the blocked vCPU on the list blocked_vcpu_on_cpu >> > + protected by blocked_vcpu_on_cpu_lock, when VT-d hardware >> issues >> > + wakeup notification event since external interrupts from the >> > + assigned devices happens, we will find the vCPU on the list to >> > + wakeup. >> > diff --git a/arch/x86/include/asm/kvm_host.h >> b/arch/x86/include/asm/kvm_host.h >> > index 0ddd353..304fbb5 100644 >> > --- a/arch/x86/include/asm/kvm_host.h >> > +++ b/arch/x86/include/asm/kvm_host.h >> > @@ -552,6 +552,8 @@ struct kvm_vcpu_arch { >> > */ >> > bool write_fault_to_shadow_pgtable; >> > >> > + bool halted; >> > + >> > /* set at EPT violation at this point */ >> > unsigned long exit_qualification; >> > >> > @@ -864,6 +866,17 @@ struct kvm_x86_ops { >> > /* pmu operations of sub-arch */ >> > const struct kvm_pmu_ops *pmu_ops; >> > >> > + /* >> > + * Architecture specific hooks for vCPU blocking due to >> > + * HLT instruction. >> > + * Returns for .pre_block(): >> > + * - 0 means continue to block the vCPU. >> > + * - 1 means we cannot block the vCPU since some event >> > + * happens during this period, such as, 'ON' bit in >> > + * posted-interrupts descriptor is set. >> > + */ >> > + int (*pre_block)(struct kvm_vcpu *vcpu); >> > + void (*post_block)(struct kvm_vcpu *vcpu); >> > int (*update_pi_irte)(struct kvm *kvm, unsigned int host_irq, >> > uint32_t guest_irq, bool set); >> > }; >> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> > index 902a67d..9968896 100644 >> > --- a/arch/x86/kvm/vmx.c >> > +++ b/arch/x86/kvm/vmx.c >> > @@ -879,6 +879,13 @@ static DEFINE_PER_CPU(struct vmcs *, >> current_vmcs); >> > static DEFINE_PER_CPU(struct list_head, loaded_vmcss_on_cpu); >> > static DEFINE_PER_CPU(struct desc_ptr, host_gdt); >> > >> > +/* >> > + * We maintian a per-CPU linked-list of vCPU, so in wakeup_handler() we >> > + * can find which vCPU should be waken up. >> > + */ >> > +static DEFINE_PER_CPU(struct list_head, blocked_vcpu_on_cpu); >> > +static DEFINE_PER_CPU(spinlock_t, blocked_vcpu_on_cpu_lock); >> > + >> > static unsigned long *vmx_io_bitmap_a; >> > static unsigned long *vmx_io_bitmap_b; >> > static unsigned long *vmx_msr_bitmap_legacy; >> > @@ -2985,6 +2992,8 @@ static int hardware_enable(void) >> > return -EBUSY; >> > >> > INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu)); >> > + INIT_LIST_HEAD(&per_cpu(blocked_vcpu_on_cpu, cpu)); >> > + spin_lock_init(&per_cpu(blocked_vcpu_on_cpu_lock, cpu)); >> > >> > /* >> > * Now we can enable the vmclear operation in kdump >> > @@ -6121,6 +6130,25 @@ static void update_ple_window_actual_max(void) >> > ple_window_grow, INT_MIN); >> > } >> > >> > +/* >> > + * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR. >> > + */ >> > +static void wakeup_handler(void) >> > +{ >> > + struct kvm_vcpu *vcpu; >> > + int cpu = smp_processor_id(); >> > + >> > + spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu)); >> > + list_for_each_entry(vcpu, &per_cpu(blocked_vcpu_on_cpu, cpu), >> > + blocked_vcpu_list) { >> > + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); >> > + >> > + if (pi_test_on(pi_desc) == 1) >> > + kvm_vcpu_kick(vcpu); >> > + } >> > + spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu)); >> > +} >> > + >> > static __init int hardware_setup(void) >> > { >> > int r = -ENOMEM, i, msr; >> > @@ -6305,6 +6333,8 @@ static __init int hardware_setup(void) >> > kvm_x86_ops->enable_log_dirty_pt_masked = NULL; >> > } >> > >> > + kvm_set_posted_intr_wakeup_handler(wakeup_handler); >> > + >> > return alloc_kvm_area(); >> > >> > out8: >> > @@ -10430,6 +10460,126 @@ static void >> vmx_enable_log_dirty_pt_masked(struct kvm *kvm, >> > } >> > >> > /* >> > + * This routine does the following things for vCPU which is going >> > + * to be blocked if VT-d PI is enabled. >> > + * - Store the vCPU to the wakeup list, so when interrupts happen >> > + * we can find the right vCPU to wake up. >> > + * - Change the Posted-interrupt descriptor as below: >> > + * 'NDST' <-- vcpu->pre_pcpu >> > + * 'NV' <-- POSTED_INTR_WAKEUP_VECTOR >> > + * - If 'ON' is set during this process, which means at least one >> > + * interrupt is posted for this vCPU, we cannot block it, in >> > + * this case, return 1, otherwise, return 0. >> > + * >> > + */ >> > +static int vmx_pre_block(struct kvm_vcpu *vcpu) >> > +{ >> > + unsigned long flags; >> > + unsigned int dest; >> > + struct pi_desc old, new; >> > + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); >> > + >> > + if (!kvm_arch_has_assigned_device(vcpu->kvm) || >> > + !irq_remapping_cap(IRQ_POSTING_CAP)) >> > + return 0; >> > + >> > + vcpu->pre_pcpu = vcpu->cpu; >> > + spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock, >> > + vcpu->pre_pcpu), flags); >> > + list_add_tail(&vcpu->blocked_vcpu_list, >> > + &per_cpu(blocked_vcpu_on_cpu, >> > + vcpu->pre_pcpu)); >> > + spin_unlock_irqrestore(&per_cpu(blocked_vcpu_on_cpu_lock, >> > + vcpu->pre_pcpu), flags); >> > + >> > + do { >> > + old.control = new.control = pi_desc->control; >> > + >> > + /* >> > + * We should not block the vCPU if >> > + * an interrupt is posted for it. >> > + */ >> > + if (pi_test_on(pi_desc) == 1) { >> > + spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock, >> > + vcpu->pre_pcpu), flags); >> > + list_del(&vcpu->blocked_vcpu_list); >> > + spin_unlock_irqrestore( >> > + &per_cpu(blocked_vcpu_on_cpu_lock, >> > + vcpu->pre_pcpu), flags); >> > + vcpu->pre_pcpu = -1; >> > + >> > + return 1; >> > + } >> > + >> > + WARN((pi_desc->sn == 1), >> > + "Warning: SN field of posted-interrupts " >> > + "is set before blocking\n"); >> > + >> > + /* >> > + * Since vCPU can be preempted during this process, >> > + * vcpu->cpu could be different with pre_pcpu, we >> > + * need to set pre_pcpu as the destination of wakeup >> > + * notification event, then we can find the right vCPU >> > + * to wakeup in wakeup handler if interrupts happen >> > + * when the vCPU is in blocked state. >> > + */ >> > + dest = cpu_physical_id(vcpu->pre_pcpu); >> > + >> > + if (x2apic_enabled()) >> > + new.ndst = dest; >> > + else >> > + new.ndst = (dest << 8) & 0xFF00; >> > + >> > + /* set 'NV' to 'wakeup vector' */ >> > + new.nv = POSTED_INTR_WAKEUP_VECTOR; >> > + } while (cmpxchg(&pi_desc->control, old.control, >> > + new.control) != old.control); >> > + >> > + return 0; >> > +} >> > + >> > +static void vmx_post_block(struct kvm_vcpu *vcpu) >> > +{ >> > + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); >> > + struct pi_desc old, new; >> > + unsigned int dest; >> > + unsigned long flags; >> > + >> > + if (!kvm_arch_has_assigned_device(vcpu->kvm) || >> > + !irq_remapping_cap(IRQ_POSTING_CAP)) >> > + return; >> > + >> > + do { >> > + old.control = new.control = pi_desc->control; >> > + >> > + dest = cpu_physical_id(vcpu->cpu); >> > + >> > + if (x2apic_enabled()) >> > + new.ndst = dest; >> > + else >> > + new.ndst = (dest << 8) & 0xFF00; >> > + >> > + /* Allow posting non-urgent interrupts */ >> > + new.sn = 0; >> > + >> > + /* set 'NV' to 'notification vector' */ >> > + new.nv = POSTED_INTR_VECTOR; >> > + } while (cmpxchg(&pi_desc->control, old.control, >> > + new.control) != old.control); >> > + >> > + if(vcpu->pre_pcpu != -1) { >> > + spin_lock_irqsave( >> > + &per_cpu(blocked_vcpu_on_cpu_lock, >> > + vcpu->pre_pcpu), flags); >> > + list_del(&vcpu->blocked_vcpu_list); >> > + spin_unlock_irqrestore( >> > + &per_cpu(blocked_vcpu_on_cpu_lock, >> > + vcpu->pre_pcpu), flags); >> > + vcpu->pre_pcpu = -1; >> > + } >> > +} >> > + >> > +/* >> > * vmx_update_pi_irte - set IRTE for Posted-Interrupts >> > * >> > * @kvm: kvm >> > @@ -10620,6 +10770,9 @@ static struct kvm_x86_ops vmx_x86_ops = { >> > .flush_log_dirty = vmx_flush_log_dirty, >> > .enable_log_dirty_pt_masked = vmx_enable_log_dirty_pt_masked, >> > >> > + .pre_block = vmx_pre_block, >> > + .post_block = vmx_post_block, >> > + >> > .pmu_ops = &intel_pmu_ops, >> > >> > .update_pi_irte = vmx_update_pi_irte, >> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> > index 58688aa..46f55b2 100644 >> > --- a/arch/x86/kvm/x86.c >> > +++ b/arch/x86/kvm/x86.c >> > @@ -5869,7 +5869,12 @@ int kvm_vcpu_halt(struct kvm_vcpu *vcpu) >> > { >> > ++vcpu->stat.halt_exits; >> > if (irqchip_in_kernel(vcpu->kvm)) { >> > - vcpu->arch.mp_state = KVM_MP_STATE_HALTED; >> > + /* Handle posted-interrupt when vCPU is to be halted */ >> > + if (!kvm_x86_ops->pre_block || >> > + kvm_x86_ops->pre_block(vcpu) == 0) { >> > + vcpu->arch.halted = true; >> > + vcpu->arch.mp_state = KVM_MP_STATE_HALTED; >> > + } >> > return 1; >> > } else { >> > vcpu->run->exit_reason = KVM_EXIT_HLT; >> > @@ -6518,6 +6523,20 @@ static int vcpu_enter_guest(struct kvm_vcpu >> *vcpu) >> > kvm_vcpu_reload_apic_access_page(vcpu); >> > } >> > >> > + /* >> > + * KVM_REQ_EVENT is not set when posted interrupts are set by >> > + * VT-d hardware, so we have to update RVI unconditionally. >> > + */ >> > + if (kvm_lapic_enabled(vcpu)) { >> > + /* >> > + * Update architecture specific hints for APIC >> > + * virtual interrupt delivery. >> > + */ >> > + if (kvm_x86_ops->hwapic_irr_update) >> > + kvm_x86_ops->hwapic_irr_update(vcpu, >> > + kvm_lapic_find_highest_irr(vcpu)); >> > + } >> > + >> > if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) { >> > kvm_apic_accept_events(vcpu); >> > if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) { >> > @@ -6534,13 +6553,6 @@ static int vcpu_enter_guest(struct kvm_vcpu >> *vcpu) >> > kvm_x86_ops->enable_irq_window(vcpu); >> > >> > if (kvm_lapic_enabled(vcpu)) { >> > - /* >> > - * Update architecture specific hints for APIC >> > - * virtual interrupt delivery. >> > - */ >> > - if (kvm_x86_ops->hwapic_irr_update) >> > - kvm_x86_ops->hwapic_irr_update(vcpu, >> > - kvm_lapic_find_highest_irr(vcpu)); >> > update_cr8_intercept(vcpu); >> > kvm_lapic_sync_to_vapic(vcpu); >> > } >> > @@ -6711,10 +6723,31 @@ static int vcpu_run(struct kvm_vcpu *vcpu) >> > >> > for (;;) { >> > if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE && >> > - !vcpu->arch.apf.halted) >> > + !vcpu->arch.apf.halted) { >> > + /* >> > + * For some cases, we can get here with >> > + * vcpu->arch.halted being true. >> > + */ >> > + if (kvm_x86_ops->post_block && vcpu->arch.halted) { >> > + kvm_x86_ops->post_block(vcpu); >> > + vcpu->arch.halted = false; >> > + } >> > + >> > r = vcpu_enter_guest(vcpu); >> > - else >> > + } else { >> > r = vcpu_block(kvm, vcpu); >> > + >> > + /* >> > + * post_block() must be called after >> > + * pre_block() which is called in >> > + * kvm_vcpu_halt(). >> > + */ >> > + if (kvm_x86_ops->post_block && vcpu->arch.halted) { >> > + kvm_x86_ops->post_block(vcpu); >> > + vcpu->arch.halted = false; >> > + } >> > + } >> > + >> > if (r <= 0) >> > break; >> > >> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >> > index feba1fb..bf462e7 100644 >> > --- a/include/linux/kvm_host.h >> > +++ b/include/linux/kvm_host.h >> > @@ -231,6 +231,9 @@ struct kvm_vcpu { >> > unsigned long requests; >> > unsigned long guest_debug; >> > >> > + int pre_pcpu; >> > + struct list_head blocked_vcpu_list; >> > + >> > struct mutex mutex; >> > struct kvm_run *run; >> > >> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> > index 8b8a444..191c7eb 100644 >> > --- a/virt/kvm/kvm_main.c >> > +++ b/virt/kvm/kvm_main.c >> > @@ -220,6 +220,9 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm >> *kvm, unsigned id) >> > init_waitqueue_head(&vcpu->wq); >> > kvm_async_pf_vcpu_init(vcpu); >> > >> > + vcpu->pre_pcpu = -1; >> > + INIT_LIST_HEAD(&vcpu->blocked_vcpu_list); >> > + >> > page = alloc_page(GFP_KERNEL | __GFP_ZERO); >> > if (!page) { >> > r = -ENOMEM; >> > -- >> > 2.1.0 >> > >> > -- >> > To unsubscribe from this list: send the line "unsubscribe kvm" in >> > the body of a message to majordomo@xxxxxxxxxxxxxxx >> > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
