Re: [Xen-devel] [PATCH v11 08/34] ARM: GIC: Add checks for NULL pointer pending_irq's

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 9 Jun 2017, Andre Przywara wrote:
> For LPIs the struct pending_irq's are dynamically allocated and the
> pointers will be stored in a radix tree. Since an LPI can be "unmapped"
> at any time, teach the VGIC how to deal with irq_to_pending() returning
> a NULL pointer.
> We just do nothing in this case or clean up the LR if the virtual LPI
> number was still in an LR.
> 
> Those are all call sites for irq_to_pending(), as per:
> "git grep irq_to_pending", and their evaluations:
> (PROTECTED means: added NULL check and bailing out)
> 
>     xen/arch/arm/gic.c:
> gic_route_irq_to_guest(): only called for SPIs, added ASSERT()
> gic_remove_irq_from_guest(): only called for SPIs, added ASSERT()
> gic_remove_from_lr_pending(): PROTECTED, called within VCPU VGIC lock
> gic_raise_inflight_irq(): PROTECTED, called under VCPU VGIC lock
> gic_raise_guest_irq(): PROTECTED, called under VCPU VGIC lock
> gic_update_one_lr(): PROTECTED, called under VCPU VGIC lock
> 
>     xen/arch/arm/vgic.c:
> vgic_migrate_irq(): not called for LPIs (virtual IRQs), added ASSERT()
> arch_move_irqs(): not iterating over LPIs, LPI ASSERT already in place
> vgic_disable_irqs(): not called for LPIs, added ASSERT()
> vgic_enable_irqs(): not called for LPIs, added ASSERT()
> vgic_vcpu_inject_irq(): PROTECTED, moved under VCPU VGIC lock
> 
>     xen/include/asm-arm/event.h:
> local_events_need_delivery_nomask(): only called for a PPI, added ASSERT()
> 
>     xen/include/asm-arm/vgic.h:
> (prototype)
> 
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  xen/arch/arm/gic.c          | 26 ++++++++++++++++++++++++--
>  xen/arch/arm/vgic.c         | 21 +++++++++++++++++++++
>  xen/include/asm-arm/event.h |  3 +++
>  3 files changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> index e0c54d5..36e340b 100644
> --- a/xen/arch/arm/gic.c
> +++ b/xen/arch/arm/gic.c
> @@ -148,6 +148,7 @@ int gic_route_irq_to_guest(struct domain *d, unsigned int 
> virq,
>      /* Caller has already checked that the IRQ is an SPI */
>      ASSERT(virq >= 32);
>      ASSERT(virq < vgic_num_irqs(d));
> +    ASSERT(!is_lpi(virq));
>  
>      vgic_lock_rank(v_target, rank, flags);
>  
> @@ -184,6 +185,7 @@ int gic_remove_irq_from_guest(struct domain *d, unsigned 
> int virq,
>      ASSERT(spin_is_locked(&desc->lock));
>      ASSERT(test_bit(_IRQ_GUEST, &desc->status));
>      ASSERT(p->desc == desc);
> +    ASSERT(!is_lpi(virq));
>  
>      vgic_lock_rank(v_target, rank, flags);
>  
> @@ -420,6 +422,10 @@ void gic_raise_inflight_irq(struct vcpu *v, unsigned int 
> virtual_irq)
>  {
>      struct pending_irq *n = irq_to_pending(v, virtual_irq);
>  
> +    /* If an LPI has been removed meanwhile, there is nothing left to raise. 
> */
> +    if ( unlikely(!n) )
> +        return;
> +
>      ASSERT(spin_is_locked(&v->arch.vgic.lock));
>  
>      if ( list_empty(&n->lr_queue) )
> @@ -439,20 +445,25 @@ void gic_raise_guest_irq(struct vcpu *v, unsigned int 
> virtual_irq,
>  {
>      int i;
>      unsigned int nr_lrs = gic_hw_ops->info->nr_lrs;
> +    struct pending_irq *p = irq_to_pending(v, virtual_irq);
>  
>      ASSERT(spin_is_locked(&v->arch.vgic.lock));
>  
> +    if ( unlikely(!p) )
> +        /* An unmapped LPI does not need to be raised. */
> +        return;
> +
>      if ( v == current && list_empty(&v->arch.vgic.lr_pending) )
>      {
>          i = find_first_zero_bit(&this_cpu(lr_mask), nr_lrs);
>          if (i < nr_lrs) {
>              set_bit(i, &this_cpu(lr_mask));
> -            gic_set_lr(i, irq_to_pending(v, virtual_irq), GICH_LR_PENDING);
> +            gic_set_lr(i, p, GICH_LR_PENDING);
>              return;
>          }
>      }
>  
> -    gic_add_to_lr_pending(v, irq_to_pending(v, virtual_irq));
> +    gic_add_to_lr_pending(v, p);
>  }
>  
>  static void gic_update_one_lr(struct vcpu *v, int i)
> @@ -467,6 +478,17 @@ static void gic_update_one_lr(struct vcpu *v, int i)
>      gic_hw_ops->read_lr(i, &lr_val);
>      irq = lr_val.virq;
>      p = irq_to_pending(v, irq);
> +    /* An LPI might have been unmapped, in which case we just clean up here. 
> */
> +    if ( unlikely(!p) )
> +    {
> +        ASSERT(is_lpi(irq));
> +
> +        gic_hw_ops->clear_lr(i);
> +        clear_bit(i, &this_cpu(lr_mask));
> +
> +        return;
> +    }
> +
>      if ( lr_val.state & GICH_LR_ACTIVE )
>      {
>          set_bit(GIC_IRQ_GUEST_ACTIVE, &p->status);
> diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
> index f0d288d..1edf93d 100644
> --- a/xen/arch/arm/vgic.c
> +++ b/xen/arch/arm/vgic.c
> @@ -236,6 +236,9 @@ bool vgic_migrate_irq(struct vcpu *old, struct vcpu *new, 
> unsigned int irq)
>      unsigned long flags;
>      struct pending_irq *p;
>  
> +    /* This will never be called for an LPI, as we don't migrate them. */
> +    ASSERT(!is_lpi(irq));
> +
>      spin_lock_irqsave(&old->arch.vgic.lock, flags);
>  
>      p = irq_to_pending(old, irq);
> @@ -320,6 +323,9 @@ void vgic_disable_irqs(struct vcpu *v, uint32_t r, int n)
>      int i = 0;
>      struct vcpu *v_target;
>  
> +    /* LPIs will never be disabled via this function. */
> +    ASSERT(!is_lpi(32 * n + 31));
> +
>      while ( (i = find_next_bit(&mask, 32, i)) < 32 ) {
>          irq = i + (32 * n);
>          v_target = vgic_get_target_vcpu(v, irq);
> @@ -367,6 +373,9 @@ void vgic_enable_irqs(struct vcpu *v, uint32_t r, int n)
>      struct vcpu *v_target;
>      struct domain *d = v->domain;
>  
> +    /* LPIs will never be enabled via this function. */
> +    ASSERT(!is_lpi(32 * n + 31));
> +
>      while ( (i = find_next_bit(&mask, 32, i)) < 32 ) {
>          irq = i + (32 * n);
>          v_target = vgic_get_target_vcpu(v, irq);
> @@ -447,6 +456,12 @@ bool vgic_to_sgi(struct vcpu *v, register_t sgir, enum 
> gic_sgi_mode irqmode,
>      return true;
>  }
>  
> +/*
> + * Returns the pointer to the struct pending_irq belonging to the given
> + * interrupt.
> + * This can return NULL if called for an LPI which has been unmapped
> + * meanwhile.
> + */
>  struct pending_irq *irq_to_pending(struct vcpu *v, unsigned int irq)
>  {
>      struct pending_irq *n;
> @@ -490,6 +505,12 @@ void vgic_vcpu_inject_irq(struct vcpu *v, unsigned int 
> virq)
>      spin_lock_irqsave(&v->arch.vgic.lock, flags);
>  
>      n = irq_to_pending(v, virq);
> +    /* If an LPI has been removed, there is nothing to inject here. */
> +    if ( unlikely(!n) )
> +    {
> +        spin_unlock_irqrestore(&v->arch.vgic.lock, flags);
> +        return;
> +    }
>  
>      /* vcpu offline */
>      if ( test_bit(_VPF_down, &v->pause_flags) )
> diff --git a/xen/include/asm-arm/event.h b/xen/include/asm-arm/event.h
> index 5330dfe..caefa50 100644
> --- a/xen/include/asm-arm/event.h
> +++ b/xen/include/asm-arm/event.h
> @@ -19,6 +19,9 @@ static inline int local_events_need_delivery_nomask(void)
>      struct pending_irq *p = irq_to_pending(current,
>                                             current->domain->arch.evtchn_irq);
>  
> +    /* Does not work for LPIs. */
> +    ASSERT(!is_lpi(current->domain->arch.evtchn_irq));
> +
>      /* XXX: if the first interrupt has already been delivered, we should
>       * check whether any other interrupts with priority higher than the
>       * one in GICV_IAR are in the lr_pending queue or in the LR
> -- 
> 2.9.0
> 

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