Following the QEMU implementation, we were allocating a full page for
holding the memory of the VMGenID device, even though the device itself
is only using 16 bytes for the generation ID.

We actually don't have any reason to do that. The Linux kernel itself is
just remapping 16 bytes from the address we pass over via
ACPI/DeviceTree.

Revert to allocating 16 bytes for the VMGenID device and expose the
value via a public constant for other systems to consume.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Expose the VMGenID device via Device Tree bindings. We add a node in the
Device Tree that passes to the guest the address of the generation ID
and the interrupt we are using to notify it about generation changes,
aka snapshot events.

Signed-off-by: Sudan Landge <sudanl@amazon.com>
Signed-off-by: Babis Chalios <bchalios@amazon.es>

Our unit tests for creating FDT depends on DTB blobs that we create once
and then we use as a reference to ensure that we don't make a change
that breaks them.

Now that we pass VMGenID via DeviceTree we need to recreate these blobs,
because we modify the layout of the guest memory, so the memory node is
suddenly different.

Also, fix the code that we use to create these blobs. Since, we
re-organized crates in the repo, it was trying to write to non-existent
paths.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Linux support for VMGenID on ARM systems landed in kernel 6.10. We only
support up to kernel 6.1. So in order to be able to test VMGenID on ARM
systems we need to patch our 6.1 kernel to backport the 6.10 commits.

This commit adds the patches in our repo under
`resources/patches/vmgenid_dt` and changes rebuild.sh to patch 6.1
kernel on ARM before building it. Also, it enables `CONFIG_VMGENID` for
ARM 6.1 guest kernel.

Eventually we will switch to using guest kernels from Amazon Linux trees
hosted on Github, which they will eventually backport the relevant
patches. Once this is done we can drop the patches from our tree and we
won't need to manually patch them.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Now we have support for the device on ARM hosts as well.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Mention that Linux support VMGenID for systems with DeviceTree support
since version 6.10. Also, mention that we only support up to Linux 6.1,
so users that want to make use of VMGenID on Linux 6.1 they need to
backport DeviceTree support from 6.10.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Also, mention that users need to backport DeviceTree support for VMGenID
from mainline 6.10 down to 6.1 guest kernels.

Signed-off-by: Babis Chalios <bchalios@amazon.es>