On Mon, 2014-06-16 at 23:35 -0600, Alex Williamson wrote: > > Any idea what an off-the-shelf Asus motherboard would be doing with an > RMRR on the Intel HD graphics? > > dmar: RMRR base: 0x000000bb800000 end: 0x000000bf9fffff > IOMMU: Setting identity map for device 0000:00:02.0 [0xbb800000 - 0xbf9fffff] Hm, we should have thought of that sooner. That's quite normal — it's for the 'stolen' memory used for the framebuffer. And maybe also the GTT, and shadow GTT and other things; I forget precisely what, and it varies from one setup to another. I'd expect fairly much all systems to have an RMRR for the integrated graphics device if they have one, and your patch¹ is going to prevent assignment of those to guests... as you've presumably noticed. I'm not sure if the i915 driver is capable of fully reprogramming the hardware to completely stop using that region, to allow assignment to a guest with a 'pure' memory map and no stolen region. I suppose it must, if assignment to guests was working correctly before? Perhaps the better answer here is not to have the special cases in 'device_is_rmrr_locked()', and instead allow a device driver to call a 'iommu_release_rmrrs()' function once it's reset the hardware to *stop* doing whatever DMA the BIOS set it up with. -- David Woodhouse Open Source Technology Centre David.Woodhouse@xxxxxxxxx Intel Corporation ¹ Alex's patch prevents assignment to VM guests of *any* device which has RMRRs (reserved regions requiring an IOMMU 1:1 mapping) in its DMAR table.
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