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

[Wu, Feng]

> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] On Behalf Of Paolo
> Bonzini
> Sent: Saturday, September 19, 2015 12:07 AM
> To: Wu, Feng; Alex Williamson; joro@xxxxxxxxxx; Marcelo Tosatti
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; 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@xxxxxxxxxxxxxxxx>
> > ---
> > 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:

Indeed, I think your suggestion below is a clearer way to implement
It, I will test it and get back to you then. Thanks for the suggestion, Paolo!

Thanks,
Feng

> 
>  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)
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