[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC 12/19] xen/passthrough: iommu_deassign_device_dt: By default reassign device to nobody
On Thu, 2014-07-03 at 14:51 +0100, Julien Grall wrote: > On 07/03/2014 02:42 PM, Ian Campbell wrote: > > On Thu, 2014-07-03 at 14:01 +0100, Julien Grall wrote: > >> On 07/03/2014 01:53 PM, Ian Campbell wrote: > >>> On Thu, 2014-07-03 at 13:07 +0100, Julien Grall wrote: > >>>>>> If Xen reassigns the device to "nobody", it may receive some > >>>>>> global/context > >>>>>> fault because the transaction has failed (indeed the context has been > >>>>>> marked invalid). > >>>>> > >>>>> Can you describe here what happen in this case (I presume Xen tears down > >>>>> the iommu to quiesce them somehow?) > >>>> > >>>> The SMMU drivers will mark the different Context Bank, S2CR, SMR as > >>>> invalid. If the device is attempt to access the memory then, we will > >>>> receive an interrupt in Xen. > >>>> > >>>> Actually it's only happen once, if the device is still enabled when the > >>>> domain is shutdown. > >>> > >>> My concern was with getting a storm of such interrupts after this point. > >>> If it only happens once and any subsequent ones are damped by some means > >>> then great. > >> > >> I guess, it can happen with a buggy device trying to access memory > >> alone. But I don't think we should care about this case. > > > > Ideally such a device wouldn't be able to DoS the rest of the system. > > > > Does the SMMU not have a bit to say: deny all MMIO from this context > > without raising an exception? > > AFAIK, no. We receive a transaction fault via the global interrupt. If > we disable this interrupt we also disable potentially helpful message > when the register are misconfigured. That seems like something of a hardware shortcoming. It might be worth asking one of the ARM guys what we should do with a device which won't shut up. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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