On Tue, Mar 28, 2017 at 01:28:43AM +0000, Zhang, Xiong Y wrote: > > > Reviewed-by: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx> > > > > Entirely disabling stolen is rather massive, this stuff is supposed to > > work ... There should be special RMRR mappings in the iommu to help the > > guest access the stolen range correctly from the gpu. > > > > Which machine where does this blow up on? > > -Daniel > [Zhang, Xiong Y] Yes. Stolen memory is protected by RMRR on host. But Qemu couldn't support and don't have plan to support RMRR. Then EPT lack of mapping for stolen memory, guest couldn't access it. > The Qemu/Vfio is designed by Redhat engineers, Redhat has a white paper to explain why Qemu don't support RMRR: > https://access.redhat.com/sites/default/files/attachments/rmrr-wp1.pdf I chatted with Joonas, and he dug out the commit that changed this: commit c875d2c1b8083cd627ea0463e20bf22c2d7421ee Author: Alex Williamson <alex.williamson@xxxxxxxxxx> Date: Thu Jul 3 09:57:02 2014 -0600 iommu/vt-d: Exclude devices using RMRRs from IOMMU API domains The user of the IOMMU API domain expects to have full control of the IOVA space for the domain. RMRRs are fundamentally incompatible with that idea. We can neither map the RMRR into the IOMMU API domain, nor can we guarantee that the device won't continue DMA with the area described by the RMRR as part of the new domain. Therefore we must prevent such devices from being used by the IOMMU API. Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Please reference that commit (plus the whitepaper if you want to) in your commit message, and resubmit it with a Fixes: and cc: stable lines. This sounds like a bugfix that we need to backport. Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
