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CUDA may be an MVP, but it's a damn useful and lucrative MVP. Also, VFIO mdev can be used to virtualize graphics cards to virtual machines, both nVidia and Int

CUDA may be an MVP, but it's a damn useful and lucrative MVP. Also, VFIO mdev can be used to virtualize graphics cards to virtual machines, both nVidia and Intel. Note this is not device assignment (that's "plain" VFIO); it's the host driver exposing a partly pass-through, partly emulated device that virtualizes the host device. mdev's design was initially a Red Hat-nVidia collaboration with input from Intel (I had a small role from the Red Hat side, mostly coming up with the name :-)) and implemented by nVidia, and is used in production with both Windows and Linux guests.

monocasa 6y ago
It's not full VFIO, but it still takes hardware support. It's not really a comparable solution.
- bonzini 6y ago
  Not necessarily. Nvidia doesn't have hardware support, rather the guest driver communicates changes to the page tables to the host driver in such a way that the host can establish shadow page tables that merge the guest and host translations.
  - monocasa 6y ago
    That's not a great example though, because mdev on Nvidia is proprietary kernel module->proprietary guest kernel module->proprietary user driver. And in that case too, the ioctl layer is almost entirely maintained across the boundaries like the scheme I'm saying. You need to do that or you almost certainly get a weird impedance mismatch between guest and host that destroys perf.
    - bonzini 6y ago
      Even if nVidia's driver has a more lightweight abstraction compared to Intel's, and puts more stuff in userspace, that is not particularly relevant in my opinion: mdev only sits between host and guest driver and by design the host driver only emulates the bare minimum and multiplexes hardware resources instead. What happens in the guest between the driver and userspace does not matter to mdev.
      - monocasa 6y ago
        It is relevant, because NVidia's binary driver looks like WDDM on every platform. And Intel needs something like this either way because their hardware arch is different, and their GPU is heavily integrated with the main IOMMU.

monocasa 6y ago

It's not full VFIO, but it still takes hardware support. It's not really a comparable solution.

bonzini 6y ago
Not necessarily. Nvidia doesn't have hardware support, rather the guest driver communicates changes to the page tables to the host driver in such a way that the host can establish shadow page tables that merge the guest and host translations.
- monocasa 6y ago
  That's not a great example though, because mdev on Nvidia is proprietary kernel module->proprietary guest kernel module->proprietary user driver. And in that case too, the ioctl layer is almost entirely maintained across the boundaries like the scheme I'm saying. You need to do that or you almost certainly get a weird impedance mismatch between guest and host that destroys perf.
  - bonzini 6y ago
    Even if nVidia's driver has a more lightweight abstraction compared to Intel's, and puts more stuff in userspace, that is not particularly relevant in my opinion: mdev only sits between host and guest driver and by design the host driver only emulates the bare minimum and multiplexes hardware resources instead. What happens in the guest between the driver and userspace does not matter to mdev.
    - monocasa 6y ago
      It is relevant, because NVidia's binary driver looks like WDDM on every platform. And Intel needs something like this either way because their hardware arch is different, and their GPU is heavily integrated with the main IOMMU.