On Fri, Feb 19, 2021 at 12:30:23PM -0500, Jason Andryuk wrote: > On Wed, Oct 21, 2020 at 9:59 AM Jan Beulich <jbeulich@xxxxxxxx> wrote: > > > > On 21.10.2020 15:36, Jason Andryuk wrote: > > > On Wed, Oct 21, 2020 at 8:53 AM Jan Beulich <jbeulich@xxxxxxxx> wrote: > > >> > > >> On 21.10.2020 14:45, Jason Andryuk wrote: > > >>> On Wed, Oct 21, 2020 at 5:58 AM Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote: > > >>>> Hm, it's hard to tell what's going on. My limited experience with > > >>>> IOMMU faults on broken systems there's a small range that initially > > >>>> triggers those, and then the device goes wonky and starts accessing a > > >>>> whole load of invalid addresses. > > >>>> > > >>>> You could try adding those manually using the rmrr Xen command line > > >>>> option [0], maybe you can figure out which range(s) are missing? > > >>> > > >>> They seem to change, so it's hard to know. Would there be harm in > > >>> adding one to cover the end of RAM ( 0x04,7c80,0000 ) to ( > > >>> 0xff,ffff,ffff )? Maybe that would just quiet the pointless faults > > >>> while leaving the IOMMU enabled? > > >> > > >> While they may quieten the faults, I don't think those faults are > > >> pointless. They indicate some problem with the software (less > > >> likely the hardware, possibly the firmware) that you're using. > > >> Also there's the question of what the overall behavior is going > > >> to be when devices are permitted to access unpopulated address > > >> ranges. I assume you did check already that no devices have their > > >> BARs placed in that range? > > > > > > Isn't no-igfx already letting them try to read those unpopulated addresses? > > > > Yes, and it is for the reason that the documentation for the > > option says "If specifying `no-igfx` fixes anything, please > > report the problem." I imply from in in particular that one > > better wouldn't use it for non-development purposes of whatever > > kind. > > I stopped seeing these DMA faults, but I didn't know what made them go > away. Then when working with an older 5.4.64 kernel, I saw them > again. Eric bisected down to the 5.4.y version of mainline linux > commit: > > commit 8195400f7ea95399f721ad21f4d663a62c65036f > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Date: Mon Oct 19 11:15:23 2020 +0100 > > drm/i915: Force VT'd workarounds when running as a guest OS > > If i915.ko is being used as a passthrough device, it does not know if > the host is using intel_iommu. Mixing the iommu and gfx causes a few > issues (such as scanout overfetch) which we need to workaround inside > the driver, so if we detect we are running under a hypervisor, also > assume the device access is being virtualised. So the commit above fixes the DMA faults seen on Linux when using a i915 gfx card? Thanks for digging into this. Roger. _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
