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pvmfw: README: Document loading 

Bug: 263548441
Bug: 217709313
Test: N/A
Change-Id: I3630a713f07d1c0a26bba2ecf38d8772a1865eee
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Pierre-Clément Tosi 2023-01-09 15:58:20 +00:00
parent 2fc32451bc
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pvmfw/README.md
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@ -48,6 +48,40 @@ pvmfw currently only supports AArch64.
## Integration
### pvmfw Loading
When running pKVM, the physical memory from which the hypervisor loads pvmfw
into guest address space is not initially populated by the hypervisor itself.
Instead, it receives a pre-loaded memory region from a trusted pvmfw loader and
only then becomes responsible for protecting it. As a result, the hypervisor is
kept generic (beyond AVF) and small as it is not expected (nor necessary) for it
to know how to interpret or obtain the content of that region.
#### Android Bootloader (ABL) Support
Starting in Android T, the `PRODUCT_BUILD_PVMFW_IMAGE` build variable controls
the generation of `pvmfw.img`, a new [ABL partition][ABL-part] containing the
pvmfw binary and following the internal format of the [`boot`][boot-img]
partition, intended to be verified and loaded by ABL on AVF-compatible devices.
To support pKVM, ABL is expected to describe the region using a reserved memory
device tree node where both address and size have been properly aligned to the
page size used by the hypervisor. For example, the following node describes a
region of size `0x40000` at address `0x80000000`:
```
reserved-memory {
...
pkvm_guest_firmware {
compatible = "linux,pkvm-guest-firmware-memory";
reg = <0x0 0x80000000 0x40000>;
no-map;
}
}
```
[ABL-part]: https://source.android.com/docs/core/architecture/bootloader/partitions
[boot-img]: https://source.android.com/docs/core/architecture/bootloader/boot-image-header
### Configuration Data
As part of the process of loading pvmfw, the loader (typically the Android