Re: [PATCH 2/3] virtio ring implementation

[Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>]

On Tue, 2007-09-25 at 19:15 +0200, Dor Laor wrote:
> At the moment it's not good enough, there is a potential race were the
> guest optimistically turn off
> the VRING_AVAIL_F_NO_INTERRUPT in the vring_restart and afterwards
> finds there are more_used so
> it consume them in the poll function. 
> If in the middle, packets arrive the host will see the flag is off and
> send irq.
> In that case the above irq handler will report IRQ_NONE.

Good point.  On the one hand, reporting IRQ_NONE occasionally is not
fatal.  On the other, it'd be nice to get this right.

> It's also not trivial to cancel the optimistic approach in the restart
> function since then there might be another race
> that will result in missing irq reaching the guest.

I did it optimistically because otherwise we need two barriers (and
still have a window).

> I'll try to think of something better than a hypercall for switching
> irq on/off.

Erk.  That would be v. bad...

Thanks,
Rusty.


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