[Bug 2072381] Re: NVMe show-regs command forcibly reboots ARM-based VM

[Heitor Alves de Siqueira]

Thanks for the help, Dan!

I've pushed a patch upstream into nvme-cli [0] to fix the 64-bit time_t
issues, I'll see to getting it into Debian/Ubuntu with Chengen's patch.

[0] https://github.com/linux-nvme/nvme-cli/commit/fa0296794e49

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https://bugs.launchpad.net/bugs/2072381

Title:
  NVMe show-regs command forcibly reboots ARM-based VM

Status in nvme-cli package in Ubuntu:
  Fix Committed
Status in nvme-cli source package in Focal:
  In Progress
Status in nvme-cli source package in Jammy:
  In Progress
Status in nvme-cli source package in Mantic:
  Won't Fix
Status in nvme-cli source package in Noble:
  In Progress
Status in nvme-cli source package in Oracular:
  Fix Committed

Bug description:
  [Impact]
  The ARM-based VM will reboot after executing the 'nvme show-regs' command.

  [Fix]
  There is an upstream commit that fixed this issue:

  commit fa5a46cc25b884a61a14f06e6693373bcefff29d
  Author:     Oliver Upton <oliver.upton at linux.dev>
  Date: Thu Jul 4 19:59:26 2024 +0200

      common.h: Avoid using unsupported load/store instructions in arm64
  VMs

      Using nvme show-regs within a VM on arm64 can sometimes lead to VM
      termination.

      To answer why this happens: one of the deficiencies of the Arm
      architecture is that there exists a range of load/store instructions
      that have insufficient decode information for traps taken to the
      hypervisor. KVM, for example, may raise an external abort or outright
      terminate the VM depending on the configuration.

      This is a known problem on the kernel side, and is fixed by using
      assembly MMIO accessors w/ 'safe' load/store instructions. So do
      exactly that, providing arm64-specific accessors and falling back to
      plain old volatile pointer accesses for other architectures.

      Reported-by: William Butler <wab at google.com>
      Signed-off-by: Oliver Upton <oliver.upton at linux.dev>

  [Test Plan]
  Execute the command 'nvme show-regs /dev/nvme0' to confirm if it functions correctly.

  [Where problems could occur]
  The patch fixes the issue by using assembly code to access MMIO on ARM, while keeping the original approach on other platforms. If the patch encounters any issues, it will only impact the functionality of displaying register data on ARM-based platforms.

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