[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] IOMMU: don't disable bus mastering on faults for devices used by Xen or Dom0
>>> On 06.11.12 at 13:06, Dario Faggioli <dario.faggioli@xxxxxxxxxx> wrote: > On Tue, 2012-11-06 at 09:44 +0000, Tim Deegan wrote: >> > In the context of analyzing the situation described in >> > "iommu=dom0-passthrough behavior" >> > (http://lists.xen.org/archives/html/xen-devel/2012-11/msg00140.html) >> > I suppressed the IOMMU setup for some device in Dom0, and >> > was quite puzzled to find that only a single fault would occur. >> >> I think it would be better to allow some small number of faults per >> device before disabling it rather than give dom0 carte blanche. >> >> This check is really there to stop a mad device from hosing the system >> rather than to contain a malicious OS, and a properly out-of-control >> device needs to be stopped or it will livelock Xen with iommu faults. >> In a uniprocessor system, dom0 might never get the chance to fix it. >> > Right. But moving the fault handling code to softirq should have already > helped solving/mitigating that, hasn't it? It helps keeping Xen alive, but doesn't for any specific domain (including Dom0). > When implementing and testing that, I wasn't able to reproduce any > livelock situation (although I can't exclude that to be at least partly > due to my inexperience, especially at the time, with I/O > virtualization)... Jan, have you (after killing the 'disable > bus-mastering part' of course)? No, I haven't - you'd have to have a device that doesn't stop I/O after a finite amount was done (or program one that way, e.g. by handing it a cyclic list of SG descriptors or alike). Wasn't it at your (Citrix) end that the problem was actually observed/reported? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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