Date:	Fri, 1 Jul 2016 09:57:25 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	"Lan, Tianyu" <tianyu.lan@...el.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Jan Kiszka <jan.kiszka@....de>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1 02/11] KVM: x86: add kvm_apic_map_get_dest_lapic



On 30/06/2016 22:54, Radim Krčmář wrote:
> kvm_irq_delivery_to_apic_fast and kvm_intr_is_single_vcpu_fast both
> compute the interrupt destination.  Factor the code.
> 
> 'struct kvm_lapic **dst = NULL' had to be added to silence GCC.
> GCC might complain about potential NULL access in the future, because it
> missed conditions that avoided uninitialized uses of dst.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  v1: improved comment for kvm_apic_map_get_dest_lapic() [Peter]
> 
>  arch/x86/kvm/lapic.c | 241 ++++++++++++++++++++++-----------------------------
>  1 file changed, 103 insertions(+), 138 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 22a6474af220..238b87b068db 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -671,14 +671,98 @@ static void kvm_apic_disabled_lapic_found(struct kvm *kvm)
>  	}
>  }
>  
> +/* Return true if the interrupt can be handled by using *bitmap as index mask
> + * for valid destinations in *dst array.
> + * Return false if kvm_apic_map_get_dest_lapic did nothing useful.
> + * Note: we may have zero kvm_lapic destinations when we return true, which
> + * means that the interrupt should be dropped.  In this case, *bitmap would be
> + * zero and *dst undefined.
> + */
> +static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm, struct kvm_lapic *src,
> +		struct kvm_lapic_irq *irq, struct kvm_apic_map *map,
> +		struct kvm_lapic ***dst, unsigned long *bitmap)
> +{
> +	int i, lowest;
> +	bool x2apic_ipi;
> +	u16 cid;
> +
> +	if (irq->shorthand == APIC_DEST_SELF) {
> +		*dst = &src;

This is not valid, &src dies as soon as you leave the function.  You
need to pass &src into kvm_apic_map_get_dest_lapic and here do something
like

	if (irq->shorthand) {
		if (irq->shorthand == APIC_DEST_SELF && p_src) {
			*dst = p_src;
			*bitmap = 1;
			return true;
		}
		return false;
	}

If it's not too hard, I'd like to have patch 4 before this one.

Paolo

> +		*bitmap = 1;
> +		return true;
> +	} else if (irq->shorthand)
> +		return false;
> +
> +	x2apic_ipi = src && apic_x2apic_mode(src);
> +	if (irq->dest_id == (x2apic_ipi ? X2APIC_BROADCAST : APIC_BROADCAST))
> +		return false;
> +
> +	if (!map)
> +		return false;
> +
> +	if (irq->dest_mode == APIC_DEST_PHYSICAL) {
> +		if (irq->dest_id >= ARRAY_SIZE(map->phys_map)) {
> +			*bitmap = 0;
> +		} else {
> +			*dst = &map->phys_map[irq->dest_id];
> +			*bitmap = 1;
> +		}
> +		return true;
> +	}
> +
> +	if (!kvm_apic_logical_map_valid(map))
> +		return false;
> +
> +	apic_logical_id(map, irq->dest_id, &cid, (u16 *)bitmap);
> +
> +	if (cid >= ARRAY_SIZE(map->logical_map)) {
> +		*bitmap = 0;
> +		return true;
> +	}
> +
> +	*dst = map->logical_map[cid];
> +
> +	if (!kvm_lowest_prio_delivery(irq))
> +		return true;
> +
> +	if (!kvm_vector_hashing_enabled()) {
> +		lowest = -1;
> +		for_each_set_bit(i, bitmap, 16) {
> +			if (!(*dst)[i])
> +				continue;
> +			if (lowest < 0)
> +				lowest = i;
> +			else if (kvm_apic_compare_prio((*dst)[i]->vcpu,
> +						(*dst)[lowest]->vcpu) < 0)
> +				lowest = i;
> +		}
> +	} else {
> +		if (!*bitmap)
> +			return true;
> +
> +		lowest = kvm_vector_to_index(irq->vector, hweight16(*bitmap),
> +				bitmap, 16);
> +
> +		if (!(*dst)[lowest]) {
> +			kvm_apic_disabled_lapic_found(kvm);
> +			*bitmap = 0;
> +			return true;
> +		}
> +	}
> +
> +	*bitmap = (lowest >= 0) ? 1 << lowest : 0;
> +
> +	return true;
> +}
> +
>  bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
>  		struct kvm_lapic_irq *irq, int *r, struct dest_map *dest_map)
>  {
>  	struct kvm_apic_map *map;
> -	unsigned long bitmap = 1;
> -	struct kvm_lapic **dst;
> +	unsigned long bitmap;
> +	struct kvm_lapic **dst = NULL;
>  	int i;
> -	bool ret, x2apic_ipi;
> +	bool ret;
>  
>  	*r = -1;
>  
> @@ -687,86 +771,19 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
>  		return true;
>  	}
>  
> -	if (irq->shorthand)
> -		return false;
> -
> -	x2apic_ipi = src && apic_x2apic_mode(src);
> -	if (irq->dest_id == (x2apic_ipi ? X2APIC_BROADCAST : APIC_BROADCAST))
> -		return false;
> -
> -	ret = true;
>  	rcu_read_lock();
>  	map = rcu_dereference(kvm->arch.apic_map);
>  
> -	if (!map) {
> -		ret = false;
> -		goto out;
> -	}
> -
> -	if (irq->dest_mode == APIC_DEST_PHYSICAL) {
> -		if (irq->dest_id >= ARRAY_SIZE(map->phys_map))
> -			goto out;
> -
> -		dst = &map->phys_map[irq->dest_id];
> -	} else {
> -		u16 cid;
> -
> -		if (!kvm_apic_logical_map_valid(map)) {
> -			ret = false;
> -			goto out;
> +	ret = kvm_apic_map_get_dest_lapic(kvm, src, irq, map, &dst, &bitmap);
> +	if (ret)
> +		for_each_set_bit(i, &bitmap, 16) {
> +			if (!dst[i])
> +				continue;
> +			if (*r < 0)
> +				*r = 0;
> +			*r += kvm_apic_set_irq(dst[i]->vcpu, irq, dest_map);
>  		}
>  
> -		apic_logical_id(map, irq->dest_id, &cid, (u16 *)&bitmap);
> -
> -		if (cid >= ARRAY_SIZE(map->logical_map))
> -			goto out;
> -
> -		dst = map->logical_map[cid];
> -
> -		if (!kvm_lowest_prio_delivery(irq))
> -			goto set_irq;
> -
> -		if (!kvm_vector_hashing_enabled()) {
> -			int l = -1;
> -			for_each_set_bit(i, &bitmap, 16) {
> -				if (!dst[i])
> -					continue;
> -				if (l < 0)
> -					l = i;
> -				else if (kvm_apic_compare_prio(dst[i]->vcpu,
> -							dst[l]->vcpu) < 0)
> -					l = i;
> -			}
> -			bitmap = (l >= 0) ? 1 << l : 0;
> -		} else {
> -			int idx;
> -			unsigned int dest_vcpus;
> -
> -			dest_vcpus = hweight16(bitmap);
> -			if (dest_vcpus == 0)
> -				goto out;
> -
> -			idx = kvm_vector_to_index(irq->vector,
> -				dest_vcpus, &bitmap, 16);
> -
> -			if (!dst[idx]) {
> -				kvm_apic_disabled_lapic_found(kvm);
> -				goto out;
> -			}
> -
> -			bitmap = (idx >= 0) ? 1 << idx : 0;
> -		}
> -	}
> -
> -set_irq:
> -	for_each_set_bit(i, &bitmap, 16) {
> -		if (!dst[i])
> -			continue;
> -		if (*r < 0)
> -			*r = 0;
> -		*r += kvm_apic_set_irq(dst[i]->vcpu, irq, dest_map);
> -	}
> -out:
>  	rcu_read_unlock();
>  	return ret;
>  }
> @@ -789,8 +806,9 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
>  			struct kvm_vcpu **dest_vcpu)
>  {
>  	struct kvm_apic_map *map;
> +	unsigned long bitmap;
> +	struct kvm_lapic **dst = NULL;
>  	bool ret = false;
> -	struct kvm_lapic *dst = NULL;
>  
>  	if (irq->shorthand)
>  		return false;
> @@ -798,69 +816,16 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
>  	rcu_read_lock();
>  	map = rcu_dereference(kvm->arch.apic_map);
>  
> -	if (!map)
> -		goto out;
> +	if (kvm_apic_map_get_dest_lapic(kvm, NULL, irq, map, &dst, &bitmap) &&
> +			hweight16(bitmap) == 1) {
> +		unsigned long i = find_first_bit(&bitmap, 16);
>  
> -	if (irq->dest_mode == APIC_DEST_PHYSICAL) {
> -		if (irq->dest_id == 0xFF)
> -			goto out;
> -
> -		if (irq->dest_id >= ARRAY_SIZE(map->phys_map))
> -			goto out;
> -
> -		dst = map->phys_map[irq->dest_id];
> -		if (dst && kvm_apic_present(dst->vcpu))
> -			*dest_vcpu = dst->vcpu;
> -		else
> -			goto out;
> -	} else {
> -		u16 cid;
> -		unsigned long bitmap = 1;
> -		int i, r = 0;
> -
> -		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;
> -
> -		if (kvm_vector_hashing_enabled() &&
> -				kvm_lowest_prio_delivery(irq)) {
> -			int idx;
> -			unsigned int dest_vcpus;
> -
> -			dest_vcpus = hweight16(bitmap);
> -			if (dest_vcpus == 0)
> -				goto out;
> -
> -			idx = kvm_vector_to_index(irq->vector, dest_vcpus,
> -						  &bitmap, 16);
> -
> -			dst = map->logical_map[cid][idx];
> -			if (!dst) {
> -				kvm_apic_disabled_lapic_found(kvm);
> -				goto out;
> -			}
> -
> -			*dest_vcpu = dst->vcpu;
> -		} else {
> -			for_each_set_bit(i, &bitmap, 16) {
> -				dst = map->logical_map[cid][i];
> -				if (++r == 2)
> -					goto out;
> -			}
> -
> -			if (dst && kvm_apic_present(dst->vcpu))
> -				*dest_vcpu = dst->vcpu;
> -			else
> -				goto out;
> +		if (dst[i]) {
> +			*dest_vcpu = dst[i]->vcpu;
> +			ret = true;
>  		}
>  	}
>  
> -	ret = true;
> -out:
>  	rcu_read_unlock();
>  	return ret;
>  }
> 

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