On Thu, Feb 02, 2017 at 04:39:35PM +0000, Marc Zyngier wrote: > On 02/02/17 16:16, Michael S. Tsirkin wrote: > > On Thu, Feb 02, 2017 at 01:34:03PM +0000, Robin Murphy wrote: > >> On 02/02/17 11:26, Will Deacon wrote: > >>> On Wed, Feb 01, 2017 at 09:19:22PM +0200, Michael S. Tsirkin wrote: > >>>> On Wed, Feb 01, 2017 at 06:27:09PM +0000, Will Deacon wrote: > >>>>> On Wed, Feb 01, 2017 at 08:09:21PM +0200, Michael S. Tsirkin wrote: > >>>>>> I'd like to do that instead. It's fastboot doing the unreasonable thing > >>>>>> here and deviating from what every other legacy device without exception > >>>>>> did for years. If this means fastboot will need to update to virtio 1, > >>>>>> all the better. > >>>>> > >>>>> The problem still exists with virtio 1, unless we require that the > >>>>> "dma-coherent" property is set/unset correctly when VIRTIO_F_IOMMU_PLATFORM > >>>>> is advertised by the device (which is what I suggested in my reply). > >>>> > >>>> I'm not ignoring that, but I need to understand that part a bit better. > >>>> I'll reply to that patch in a day or two after looking at how _CCA is > >>>> supposed to work. > >>> > >>> Thanks. I do think that whatever solution we come up with for virtio 1 > >>> should influence what we do for legacy. > >>> > >>>>> We can't detect the fastmodel, > >>>> > >>>> Surely, it puts a hardware id somewhere? I think you mean > >>>> fastmodel isn't always affected, right? > >>> > >>> I don't think there's a hardware ID. The thing is, the fastmodel is a > >>> toolkit for building all sorts of platforms: you can chop and change > >>> the CPUs, the peripherals, the memory, the interrupt controller, the > >>> interconnect etc. Pretty much everything can be customised. So, for > >>> any fastmodel configuration that places virtio upstream of the SMMU > >>> (which is common, because virtio is one of the few DMA-capable peripherals > >>> that the fastmodel supports), we need to do something special. > >>> > >>>> I'd like to see basically > >>>> > >>>> if (fastmodel) > >>>> a pile of special work-arounds > >>>> else > >>>> not less hacky but more common virtio work-arounds > >>>> > >>>> :) > >>>> > >>>> And then I can apply whatever comes from @arm.com and not > >>>> worry about breaking actual hardware. > >>> > >>> What we could do is call iommu_group_get(&vdev->dev) for legacy > >> > >> Actually, that should be vdev->dev.parent - I'm now not sure quite what > >> I managed to successfully test yesterday, but apparently it wasn't this > >> patch :( > >> > >>> devices if CONFIG_ARM64. If that returns non-NULL, then we know that > >>> the device is upstream of an SMMU, which means it must be the fastmodel. > >> > >> We can boot 32-bit kernels on models, so I'd be inclined to keep > >> CONFIG_ARM included, but I do tend to agree that explicitly checking for > >> an IOMMU is probably the cleanest approach if we reposition this as a > >> more specific quirk. I'll split apart the "Fast Models are wacky" vs. > >> "uh-oh device coherency" aspects and spin a v2 so that we can > >> (hopefully) sort the regression out ASAP. > >> > >> Robin. > >> > >>> > >>> Will > >>> > > > > I still think the right thing to do for this platform is to add an API > > for driver to say "disable protection for this device and allow > > this device 1:1 access to all memory". This > > would make both platforms which bypass the iommu and platforms that > > don't happy as PA == dma address. > > Hi Michael, > > What would this API be? A command-line option? A magic DT property? Yet > another ACPI bodge? Given the type of HW platform we're looking at, > changing the firmware to expose a new property is unlikely to be practical. No - I mean an internal kernel API that the legacy driver can call. > My point is: we have all the required information in the kernel to do > the right thing without asking the user to change anything in their > existing setup. With this (admittedly unpleasant) change, we can make > things work for both IOMMU and non-IOMMU setups, dma-coherent or not. > And frankly, it doesn't look much worse than the Xen thing that sits a > few lines above. > > Am I missing something more obvious than "you should use a flying car > instead"? ;-) > > Thanks, > > M. I agree we should try to do the right thing. Using an MMU to protect against a hypervisor is a futile effort though. It simply makes sense to allow virtio access to all of memory. virtio 1 has a flag to control that to handle weird corner cases. > -- > Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
