On 2020.10.16 17:19:19 +0200, Stefan Fritsch wrote: > Hi, > > if Linux is running as a guest and the host is doing igd-pass-thorugh with > VT-d enabled, the i915 driver does not work all that great. The most > obvious problem is that there are dozens of 'Fault errors on pipe A' > errrors logged per second, but depending on the hardware there can be > other issues, too. I will send a patch to rate-limit that message in a > separate mail. > > The i915 has various quirks for VT-d and these should be enabled even if > Linux is running as a guest and does itself have iommu enabled. I have > checked that making intel_vtd_active() form i915_drv.h return true makes > the error messages go away. How could Linux detect this situation? Maybe > simply check the Hypervisor cpuid bit? Or would you prefer a module > parameter, or a combination of both? Or is there another way to detect > that VT-d is enabled for the igd device? > I think that's right, although I haven't tried to force intel_vtd_active() for guest, but I did see those fault errors on some machine. You can use hypervisor cpuid bit, and need to seperate case for GVT which is detected by intel_vgpu_active(), but I'm not sure if this should be taken in nested case, suppose those quirks should still work? -- $gpg --keyserver wwwkeys.pgp.net --recv-keys 4D781827
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