Re: [RFC][PATCH 0/2] Fix guest shared interrupt with in-kernel irqchip

[Avi Kivity <avi@redhat.com>]

Yang, Sheng wrote:
> To deal with guest shared interrupt bug in in-kernel irqchip, we should:
>
> 1. Identify each level trig interrupt source.
> 2. Implement logical OR on the same IRQ line for each interrupt source.
>
> Here I chose a simple method: the caller of kvm_set_irq() has responsiblity
> to identify interrupt sources, and IOAPIC/PIC ensure logical OR on IRQ line.
>   

The downside is that every caller has to do this edge detection.

How about allocating a vector of u32s (one per irq), and each source 
will allocate a bit within this vector.  The 'or' operation becomes 
(word != 0).

For example:

   irq_src = kvm_irq_allocate_source(kvm);  /* allocate bit within irq 
vector */

    ...
 
   kvm_set_irq(kvm, irq, 1, irq_src);

kvm_set_irq(...)
{
    // locking?
    if (level)
        set_bit(irq_src, &kvm->irq_state[irq]);
    else
        clear_bit(irq_src, &kvm->irq_state[irq]);
   kvm_pic_set_irq(kvm, irq, !!kvm->irq_state[irq]);
   kvm_ioapic_set_irq(kvm, irq, !!kvm->irq_state[irq]);
}

kvm_irq_allocate_source(kvm)
{
     irq_src = find_first_clear_bit(kvm->irq_sources);
     set_bit(irq_src, &kvm->irq_sources);
     return irq_src;
}

This also keeps the pic and ioapic out of the picture, which is good.  
It also allows us to implement negative polarity easily in the future.

-- 
error compiling committee.c: too many arguments to function