[Xen-devel] Question, Lock of pending_irq struct in Xen ARM.

[ììì <supsup5642@xxxxxxxxx>]

HI.

I'm now modifying GIC in Xen 4.5.0. 

I have some question about lock of pending_irq struct in Xen ARM. 

 

pending_irq of SGI and PPI is stored in 'vcpu struct'. (IRQ num 0 ~ 31)

pending_irq of SPI is stored in 'domain struct'. (IRQ num 32 ~ )

 

For accessing pending_irq struct, Xen use 'irq_to_pending(struct vcpu *v, int  irq)' function.

irq_to_pending function return proper pending_irq depending on IRQ number. 

 

 

* 'gic_update_one_lr' function process

1) before call gic_update_one_lr, xen acquire like this "spin_lock_irqsave(&v->arch.vgic.lock, flags)";

2) In gic_update_one_lr, get pending_irq through irq_to_pending function.

3) change state of irq_to_pending and update lr

 

When IRQ number is below 31, irq_to_pending function return pending_irq stored in vcpu struct.

It's ok to change irq_to_pending state, because &v->arch.vgic.lock acquire.

But When IRQ number is above 32, irq_to_pending function return pending_irq stored in domain struct.

And change state of irq_to_pending without domain's lock.

I think that pending_irq of SPI stored in domain struct is shared among vcpus. and need to acquire domain's lock before change pending_irq.

But why don't use domain's lock in Xen Code ??

 

Thanks.

 

* Sorry for my poor english skill..

 

 

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