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Having the virtual IOMMU created with --iommu is one thing, but we also need a way to decide if a virtio-blk device should be attached to this virtual IOMMU or not. That's why we introduce an extra option "iommu" with the value "on" or "off". By default, the device is not attached, which means "iommu=off". One side effect of this new option is that we had to introduce a new option for the disk path, simply called "path=". Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
62 lines
2.5 KiB
Markdown
62 lines
2.5 KiB
Markdown
# `cloud-hypervisor` debug IO port
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`cloud-hypervisor` uses the [`0x80`](https://www.intel.com/content/www/us/en/support/articles/000005500/boards-and-kits.html)
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I/O port to trace user defined guest events.
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Whenever the guest write one byte between `0x0` and `0xF` on this particular
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I/O port, `cloud-hypervisor` will log and timestamp that event at the `debug`
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log level.
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It is up to the guest stack to decide when and what to write to the 0x80 port
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in order to signal the host about specific events and have `cloud-hypervisor`
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log it.
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`cloud-hypervisor` defines several debug port code ranges that should be used
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for debugging specific components of the guest software stack. When logging a
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write of one of those codes to the debug port, `cloud-hypervisor` adds a
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pre-defined string to the logs.
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| Code Range | Component | Log string |
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| ---------------- | ----------- | ------------ |
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| `0x00` to `0x1f` | Firmware | `Firmware` |
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| `0x20` to `0x3f` | Bootloader | `Bootloader` |
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| `0x40` to `0x5f` | Kernel | `Kernel` |
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| `0x60` to `0x7f` | Userspace | `Userspace` |
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| `0x80` to `0xff` | Custom | `Custom` |
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One typical use case is guest boot time measurement and tracing. By writing
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different values to the debug I/O port at different boot process steps, the
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guest will have `cloud-hypervisor` generate timestamped logs of all those steps.
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That provides a basic but convenient way of measuring not only the overall guest
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boot time but all intermediate steps as well.
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## Logging
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Assuming parts of the guest software stack have been instrumented to use the
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`cloud-hypervisor` debug I/O port, we may want to gather the related logs.
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To do so we need to start `cloud-hypervisor` with the right debug level
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(`-vvv`). It is also recommended to have it log into a dedicated file in order
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to easily grep for the tracing logs (e.g.
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`--log-file /tmp/cloud-hypervisor.log`):
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```
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./target/debug/cloud-hypervisor \
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--kernel ~/rust-hypervisor-firmware/target/target/release/hypervisor-fw \
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--disk path=~/hypervisor/images/clear-30080-kvm.img \
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--cpus 4 \
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--memory size=1024M \
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--rng \
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--log-file /tmp/ch-fw.log \
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-vvv
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```
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After booting the guest, we then have to grep for the debug I/O port traces in
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the log file:
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```Shell
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$ grep "Debug I/O port" /tmp/ch-fw.log
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cloud-hypervisor: 19.762449ms: DEBUG:vmm/src/vm.rs:510 -- [Debug I/O port: Firmware code 0x0] 0.019004 seconds
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cloud-hypervisor: 403.499628ms: DEBUG:vmm/src/vm.rs:510 -- [Debug I/O port: Firmware code 0x1] 0.402744 seconds
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```
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