Re: [Xen-devel] [PATCH 7/9] arm: vgic: fix race between evtchn upcall and evtchnop_send

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-03-19 at 16:18 +0000, Stefano Stabellini wrote:
> On Wed, 6 Mar 2013, Ian Campbell wrote:
> > From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > 
> > On ARM the evtchn upcall is done by using a local PPI interrupt. However the
> > guest will clear the evtchn_upcall_pending bit before it EOIs that PPI 
> > (which
> > happens late). This means vgic_vcpu_inject_irq (called via
> > vcpu_mark_events_pending) sees the PPI as in flight and ends up not 
> > reinjecting
> > it, if this happens after the guest has finished its event channel 
> > processing
> > loop but before the EOI then we have lost the upcall.
> > 
> > We therefore also need to call gic_restore_pending_irqs on the exit to guest
> > path in order to pickup any newly inject IRQ and propagate it into a free 
> > LR.
> 
> You forgot to mention that on exit to guest, before calling
> gic_restore_pending_irqs, we check whether we need to reinject the PPI.

I inserted before "We therefore..."
    To fix this we need to check if an evtchn upcall is pending when returning 
    the guest and if so reinject the PPI.

> Aside from this, the patch is fine.

And then I took this as an Acked-by and applied. Thanks



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