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Date:	Mon, 16 Nov 2015 06:18:51 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	"pbonzini@...hat.com" <pbonzini@...hat.com>
CC:	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH] KVM: x86: Add lowest-priority support for vt-d
 posted-interrupts

Hi Paolo,

Any comments about this patch, thanks in advance!

Thanks,
Feng

> -----Original Message-----
> From: Wu, Feng
> Sent: Monday, November 9, 2015 10:47 AM
> To: pbonzini@...hat.com
> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org; Wu, Feng
> <feng.wu@...el.com>
> Subject: [PATCH] KVM: x86: Add lowest-priority support for vt-d posted-
> interrupts
> 
> Use vector-hashing to handle lowest-priority interrupts for
> posted-interrupts. As an example, modern Intel CPUs use this
> method to handle lowest-priority interrupts.
> 
> Signed-off-by: Feng Wu <feng.wu@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  2 ++
>  arch/x86/kvm/irq_comm.c         | 52
> +++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/lapic.c            | 57
> +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/lapic.h            |  2 ++
>  arch/x86/kvm/vmx.c              | 14 ++++++++--
>  5 files changed, 125 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h
> b/arch/x86/include/asm/kvm_host.h
> index 9265196..e225106 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1258,6 +1258,8 @@ bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu);
> 
>  bool kvm_intr_is_single_vcpu(struct kvm *kvm, struct kvm_lapic_irq *irq,
>  			     struct kvm_vcpu **dest_vcpu);
> +struct kvm_vcpu *kvm_intr_vector_hashing_dest(struct kvm *kvm,
> +					      struct kvm_lapic_irq *irq);
> 
>  void kvm_set_msi_irq(struct kvm_kernel_irq_routing_entry *e,
>  		     struct kvm_lapic_irq *irq);
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index 84b96d3..8156e45 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -266,6 +266,58 @@ out:
>  	return r;
>  }
> 
> +/*
> + * This routine handles lowest-priority interrupts using vector-hashing
> + * mechanism. As an example, modern Intel CPUs use this method to
> handle
> + * lowest-priority interrupts.
> + *
> + * Here is the details about the vector-hashing mechanism:
> + * 1. For lowest-priority interrupts, store all the possible destination
> + *    vCPUs in an array.
> + * 2. Use "guest vector % max number of destination vCPUs" to find the
> right
> + *    destination vCPU in the array for the lowest-priority interrupt.
> + */
> +struct kvm_vcpu *kvm_intr_vector_hashing_dest(struct kvm *kvm,
> +					      struct kvm_lapic_irq *irq)
> +
> +{
> +	unsigned long
> dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
> +	unsigned int dest_vcpus = 0;
> +	struct kvm_vcpu *vcpu;
> +	unsigned int i, mod, idx = 0;
> +
> +	vcpu = kvm_intr_vector_hashing_dest_fast(kvm, irq);
> +	if (vcpu)
> +		return vcpu;
> +
> +	memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (!kvm_apic_present(vcpu))
> +			continue;
> +
> +		if (!kvm_apic_match_dest(vcpu, NULL, irq->shorthand,
> +					irq->dest_id, irq->dest_mode))
> +			continue;
> +
> +		__set_bit(vcpu->vcpu_id, dest_vcpu_bitmap);
> +		dest_vcpus++;
> +	}
> +
> +	if (dest_vcpus == 0)
> +		return NULL;
> +
> +	mod = irq->vector % dest_vcpus;
> +
> +	for (i = 0; i <= mod; i++) {
> +		idx = find_next_bit(dest_vcpu_bitmap, KVM_MAX_VCPUS,
> idx) + 1;
> +		BUG_ON(idx >= KVM_MAX_VCPUS);
> +	}
> +
> +	return kvm_get_vcpu(kvm, idx - 1);
> +}
> +EXPORT_SYMBOL_GPL(kvm_intr_vector_hashing_dest);
> +
>  bool kvm_intr_is_single_vcpu(struct kvm *kvm, struct kvm_lapic_irq *irq,
>  			     struct kvm_vcpu **dest_vcpu)
>  {
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index ecd4ea1..4937aa4 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -816,6 +816,63 @@ out:
>  	return ret;
>  }
> 
> +struct kvm_vcpu *kvm_intr_vector_hashing_dest_fast(struct kvm *kvm,
> +						   struct kvm_lapic_irq *irq)
> +{
> +	struct kvm_apic_map *map;
> +	struct kvm_vcpu *vcpu = NULL;
> +
> +	if (irq->shorthand)
> +		return NULL;
> +
> +	rcu_read_lock();
> +	map = rcu_dereference(kvm->arch.apic_map);
> +
> +	if (!map)
> +		goto out;
> +
> +	if ((irq->dest_mode != APIC_DEST_PHYSICAL) &&
> +			kvm_lowest_prio_delivery(irq)) {
> +		u16 cid;
> +		int i, idx = 0;
> +		unsigned long bitmap = 1;
> +		unsigned int mod, dest_vcpus = 0;
> +		struct kvm_lapic **dst = NULL;
> +
> +
> +		if (!kvm_apic_logical_map_valid(map))
> +			goto out;
> +
> +		apic_logical_id(map, irq->dest_id, &cid, (u16 *)&bitmap);
> +
> +		if (cid >= ARRAY_SIZE(map->logical_map))
> +			goto out;
> +
> +		dst = map->logical_map[cid];
> +
> +		for_each_set_bit(i, &bitmap, 16) {
> +			if (!dst[i])
> +				continue;
> +
> +			dest_vcpus++;
> +		}
> +
> +		mod = irq->vector % dest_vcpus;
> +
> +		for (i = 0; i <= mod; i++) {
> +			idx = find_next_bit(&bitmap, KVM_MAX_VCPUS, idx)
> + 1;
> +			BUG_ON(idx >= KVM_MAX_VCPUS);
> +		}
> +
> +		if (kvm_apic_present(dst[idx-1]->vcpu))
> +			vcpu = dst[idx-1]->vcpu;
> +	}
> +
> +out:
> +	rcu_read_unlock();
> +	return vcpu;
> +}
> +
>  /*
>   * Add a pending IRQ into lapic.
>   * Return 1 if successfully added and 0 if discarded.
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index fde8e35d..a6a775d 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -170,4 +170,6 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu);
> 
>  bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq
> *irq,
>  			struct kvm_vcpu **dest_vcpu);
> +struct kvm_vcpu *kvm_intr_vector_hashing_dest_fast(struct kvm *kvm,
> +						   struct kvm_lapic_irq *irq);
>  #endif
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 5eb56ed..57f71ee 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -159,6 +159,9 @@ static int ple_window_actual_max =
> KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
>  static int ple_window_max        = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
>  module_param(ple_window_max, int, S_IRUGO);
> 
> +static bool __read_mostly enable_pi_vector_hashing = 1;
> +module_param(enable_pi_vector_hashing, bool, S_IRUGO);
> +
>  extern const ulong vmx_return;
> 
>  #define NR_AUTOLOAD_MSRS 8
> @@ -10702,8 +10705,15 @@ static int vmx_update_pi_irte(struct kvm *kvm,
> unsigned int host_irq,
>  		 */
> 
>  		kvm_set_msi_irq(e, &irq);
> -		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu))
> -			continue;
> +		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
> +			if ((!enable_pi_vector_hashing ||
> +				irq.delivery_mode != APIC_DM_LOWEST))
> +				continue;
> +
> +			vcpu = kvm_intr_vector_hashing_dest(kvm, &irq);
> +			if (!vcpu)
> +				continue;
> +		}
> 
>  		vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
>  		vcpu_info.vector = irq.vector;
> --
> 2.1.0

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