Re: [Xen-devel] [PATCH-4.5 v3 10/12] xen/arm: don't protect GICH and lr_queue accesses with gic.lock

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 18 Mar 2014, Julien Grall wrote:
> Hi Stefano,
> 
> On 03/18/2014 02:59 PM, Stefano Stabellini wrote:
> > On Wed, 26 Feb 2014, Julien Grall wrote:
> >> On 26/02/14 18:39, Stefano Stabellini wrote:
> >>> GICH is banked, protect accesses by disabling interrupts.
> >>> Protect lr_queue accesses with the vgic.lock only.
> >>
> >> When the interrupt is an SPI, the lr_queue is shared between every VCPU. 
> >> Using
> >> only vgic.lock seems wrong to me.
> > 
> > Even though lr_queue is a field in a struct that can be per domain for
> > irq > 32, the lr_pending queue is always per vcpu, in fact it keeps
> > track of the irqs waiting to go into lr registers, that are banked.
> > 
> 
> It might have a race between adding and removing lr_queue. For now it's
> safe because the SPIs are always routed to VCPU0 (even if the guest ask
> to route on VCPU1).
> 
> Just by reading the code, nothing protect correctly SPIs between VCPUs.
> We are only take vgic.lock, which is wrong.

Like you said, today SPIs are always routed to the same cpu.
When we'll implement IRQ migration we'll have to make sure that we take
the appropriate locks during the operation but I don't expect that this
patch is going to make things more difficult.

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