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tpuproxy: resolve FIXMEs added by cl/723723714#11453

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tpuproxy: resolve FIXMEs added by cl/723723714#11453
copybara-service[bot] wants to merge 1 commit intomasterfrom
test/cl724512151

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tpuproxy: resolve FIXMEs added by cl/723723714

  • Remove the ability to mmap VFIO group FDs. As mentioned by the deleted FIXME,
    this is consistent with Linux.

  • Use MemoryTypeUncached for VFIO_GROUP_GET_DEVICE_FD FDs. On the KVM platform,
    this ensures that e.g. writes to memory-mapped device registers occur in
    program order and without combining, and no reads are cached or issued
    speculatively. On other platforms, this has no effect since application page
    table entries are controlled by the host Linux kernel. (Technically, on the
    KVM platform, this also has no effect on Intel CPUs for reasons described in
    gvisor.dev/issue/11436.)

- Remove the ability to mmap VFIO group FDs. As mentioned by the deleted FIXME,
  this is consistent with Linux.

- Use MemoryTypeUncached for VFIO_GROUP_GET_DEVICE_FD FDs. On the KVM platform,
  this ensures that e.g. writes to memory-mapped device registers occur in
  program order and without combining, and no reads are cached or issued
  speculatively. On other platforms, this has no effect since application page
  table entries are controlled by the host Linux kernel. (Technically, on the
  KVM platform, this also has no effect on Intel CPUs for reasons described in
  gvisor.dev/issue/11436.)

PiperOrigin-RevId: 724512151
@copybara-service copybara-service bot added the exported Issue was exported automatically label Feb 8, 2025
@zhimin-z
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A friendly reminder that this PR had no activity for 120 days.

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