On Thu, Apr 18, 2024 at 09:33:31PM -0700, Elliott Mitchell wrote: > > I suspect this is a case of there is some step which is missing from > Xen's IOMMU handling. Perhaps something which Linux does during an early > DMA setup stage, but the current Xen implementation does lazily? > Alternatively some flag setting or missing step? > > I should be able to do another test approach in a few weeks, but I would > love if something could be found sooner.
Turned out to be disturbingly easy to get the first entry when it happened. Didn't even need `dbench`, it simply showed once the OS was fully loaded. I did get some additional data points. Appears this requires an AMD IOMMUv2. A test system with known functioning AMD IOMMUv1 didn't display the issue at all. (XEN) AMD-Vi: IO_PAGE_FAULT: DDDD:bb:dd.f d0 addr fffffffdf8000000 flags 0x8 I (XEN) DDDD:bb:dd.f root @ 83b5f5 (3 levels) dfn=fffffffdf8000 (XEN) L3[1f7] = 0 np I find it surprising this required "iommu=debug" to get this level of detail. This amount of output seems more appropriate for "verbose". I strongly prefer to provide snippets. There is a fair bit of output, I'm unsure which portion is most pertinent. -- (\___(\___(\______ --=> 8-) EHM <=-- ______/)___/)___/) \BS ( | ehem+sig...@m5p.com PGP 87145445 | ) / \_CS\ | _____ -O #include <stddisclaimer.h> O- _____ | / _/ 8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445
