Hi Marc,
On Wed, Jun 25, 2014 at 10:28:43AM +0100, Marc Zyngier wrote:
> When a peripheral is shared between virtual machines, its interrupt
> state becomes part of the guest's state, and must be switched accordingly.
>
> Introduce a pair of accessors (irq_get_fwd_state/irq_set_fwd_state) to
> retrieve the bits that can be of interest to KVM: pending, active, and masked.
>
> - irq_get_fwd_state returns the state of the interrupt according to a mask
> containing any of the IRQ_STATE_PENDING, IRQ_STATE_ACTIVE or IRQ_STATE_MASKED
> bits.
> - irq_set_fwd_state sets the state of the interrupt according to a similar mask.
>
> Only a forwarded interrupt can be manipulated in such a way.
[...]
> +/**
> + * irq_set_fwd_state - set the state of a forwarded interrupt.
> + * @irq: Interrupt line that is forwarded to a VM
> + * @val: State to be restored
> + * @mask: Bitmask of IRQ_FWD_STATE_* defining the valid bits in @val
> + *
> + * This call sets the state of a forwarded interrupt, depending
> + * on the mask which indicates the valid bits.
> + *
> + * This function should be called with preemption disabled if the
> + * interrupt controller has per-cpu registers.
> + */
> +int irq_set_fwd_state(unsigned int irq, u32 val, u32 mask)
> +{
> + struct irq_desc *desc;
> + struct irq_data *data;
> + struct irq_chip *chip;
> + unsigned long flags;
> +
> + desc = irq_to_desc(irq);
> + if (!desc)
> + return -EINVAL;
> +
> + data = irq_desc_get_irq_data(desc);
> + if (!irqd_irq_forwarded(data))
> + return -EINVAL;
> +
> + chip = irq_desc_get_chip(desc);
> + if (!chip->irq_set_fwd_state)
> + return -EINVAL;
> +
> + chip_bus_lock(desc);
> + raw_spin_lock_irqsave(&desc->lock, flags);
> + chip->irq_set_fwd_state(data, val, mask);
> + raw_spin_unlock_irqrestore(&desc->lock, flags);
> + chip_bus_sync_unlock(desc);
Having looked at this, I don't think you need to take the desc->lock after
all. I thought you might need it for irq_desc_get_chip, but that's not going
to change dynamically and you'd end up with a lock ordering problem against
chip_bus_lock anyway.
Will
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