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    SubjectRE: [PATCH v9 17/18] KVM: Update Posted-Interrupts Descriptor when vCPU is blocked
    Date


    > -----Original Message-----
    > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo
    > Bonzini
    > Sent: Saturday, September 19, 2015 12:07 AM
    > To: Wu, Feng; Alex Williamson; joro@8bytes.org; Marcelo Tosatti
    > Cc: iommu@lists.linux-foundation.org; linux-kernel@vger.kernel.org; KVM list;
    > Eric Auger
    > Subject: Re: [PATCH v9 17/18] KVM: Update Posted-Interrupts Descriptor when
    > vCPU is blocked
    >
    >
    >
    > On 18/09/2015 16:29, Feng Wu 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
    > >
    > > Signed-off-by: Feng Wu
    > <feng.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
    > > ---
    > > 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.
    > > + */
    >
    >
    > Feng,
    >
    > can you explain what are the reasons for this?
    >
    > Perhaps pre_block and post_block should be handled entirely in
    > vcpu_block, like this:
    >
    > static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
    > {
    > - if (!kvm_arch_vcpu_runnable(vcpu)) {
    > + if (!kvm_arch_vcpu_runnable(vcpu) &&
    > + (!kvm_x86_ops->pre_block || kvm_x86_ops->pre_block(vcpu) == 0)) {
    > srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
    > kvm_vcpu_block(vcpu);
    > vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
    > +
    > + if (kvm_x86_ops->post_block)
    > + kvm_x86_ops->post_block(vcpu);
    > +
    > if (!kvm_check_request(KVM_REQ_UNHALT, vcpu))
    > return 1;
    > }
    >
    > and removing all of your changes in kvm_vcpu_halt and vcpu_run?
    > (Full patch below my signature, only compile-tested).
    >
    > It should not matter if mp_state goes briefly to KVM_MP_STATE_HALTED and
    > from there back to KVM_MP_STATE_RUNNABLE.
    >
    > Paolo
    >
    > diff --git a/arch/x86/include/asm/kvm_host.h
    > b/arch/x86/include/asm/kvm_host.h
    > index 4a0b1a800317..5265a5522458 100644
    > --- a/arch/x86/include/asm/kvm_host.h
    > +++ b/arch/x86/include/asm/kvm_host.h
    > @@ -568,8 +568,6 @@ struct kvm_vcpu_arch {
    > */
    > bool write_fault_to_shadow_pgtable;
    >
    > - bool halted;
    > -
    > /* set at EPT violation at this point */
    > unsigned long exit_qualification;
    >
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index a2a070541318..44092cfa1c0a 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -5674,12 +5674,7 @@ int kvm_vcpu_halt(struct kvm_vcpu *vcpu)
    > {
    > ++vcpu->stat.halt_exits;
    > if (irqchip_in_kernel(vcpu->kvm)) {
    > - /* 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;
    > - }
    > + vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
    > return 1;
    > } else {
    > vcpu->run->exit_reason = KVM_EXIT_HLT;
    > @@ -6446,10 +6441,15 @@ out:
    >
    > static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
    > {
    > - if (!kvm_arch_vcpu_runnable(vcpu)) {
    > + if (!kvm_arch_vcpu_runnable(vcpu) &&
    > + (!kvm_x86_ops->pre_block || kvm_x86_ops->pre_block(vcpu) == 0)) {
    > srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
    > kvm_vcpu_block(vcpu);
    > vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
    > +
    > + if (kvm_x86_ops->post_block)
    > + kvm_x86_ops->post_block(vcpu);
    > +
    > if (!kvm_check_request(KVM_REQ_UNHALT, vcpu))
    > return 1;
    > }
    > @@ -6482,28 +6482,9 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
    > for (;;) {
    > if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
    > !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 {
    > 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)

    I tested the above patch you suggested, it works fine. Thank you! So
    do I need to resend a new version or you can handle it in your tree?

    Thanks,
    Feng



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