[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v5 3/3] xen/arm: vgic_migrate_irq: do not race against GIC_IRQ_GUEST_MIGRATING
On Mon, 3 Apr 2017, Julien Grall wrote: > Hi Stefano, > > On 31/03/17 21:24, Stefano Stabellini wrote: > > On Fri, 31 Mar 2017, Julien Grall wrote: > > > On 30/03/17 00:47, Stefano Stabellini wrote: > > > > On Fri, 3 Mar 2017, Julien Grall wrote: > > > What you described is not a data corruption to me. > > > > No, it is not, thanks to the previous two patches. The commit > > description needs an update. > > > > > > > The host IRQ will be routed > > > to the wrong pCPU and then what? The IRQ will still trigger, ok on the > > > wrong > > > pCPU, it will be slower but we are capable to handle that. > > > > > > The use case you describe would only happen if a guest is trying to change > > > the > > > routing multiple times while an interrupt is pending. So to be honest, a > > > sane > > > guest would not do that. But this would only affect stupid guest. > > > > > > So I don't think this is worth to support considering how this patch will > > > increase the code complexity in a component that is already a nightmare to > > > handle. > > > > I think we have to fix this because it is not predictable. Latency could > > be much higher, depending on who wins the race. It also uses more Xen > > resources -- the time that Xen spends to send and to handle SGIs could > > be used for something else. I think it is more important to be > > predictable than correct. Especially given that a sane guest shouldn't > > do this, I prefer to refuse a "nested" migration we cannot handle (even > > though it is a mistake) than provide unreliable latency. > > Good point. We already have a couple of place in the vGIC we don't handle and > print a message instead (see ACTIVER, I*PENDR registers). > > I would prefer to refuse "nested" migration and warn the guest. If someone > complain, then we can think about it. That's fine by me. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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