On 21/03/2024 13:32, Rob Herring wrote:
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On Wed, Mar 20, 2024 at 04:55:45PM +0000, David Woodhouse wrote:
On Wed, 2024-03-20 at 11:15 -0500, Rob Herring wrote:
On Wed, Mar 20, 2024 at 01:50:43PM +0000, David Woodhouse wrote:
On Tue, 2024-03-19 at 16:24 +0100, Krzysztof Kozlowski wrote:
On 19/03/2024 15:32, Sudan Landge wrote:
This small series of patches aims to add devicetree bindings support for
the Virtual Machine Generation ID (vmgenid) driver.
Virtual Machine Generation ID driver was introduced in commit af6b54e2b5ba
("virt: vmgenid: notify RNG of VM fork and supply generation ID") as an
ACPI only device.
We would like to extend vmgenid to support devicetree bindings because:
1. A device should not be defined as an ACPI or DT only device.
This (and the binding patch) tells me nothing about what "Virtual
Machine Generation ID driver" is and isn't really justification for
"why".
It's a reference to a memory area which the OS can use to tell whether
it's been snapshotted and restored (or 'forked'). A future submission
should have a reference to something like
https://www.qemu.org/docs/master/specs/vmgenid.html or the Microsoft
doc which is linked from there.
That doc mentions fw_cfg for which we already have a binding. Why can't
it be used/extended here?
QEMU has support for vmgenid but even they do not pass vmgenid directly
to the guest kernel using fw_cfg. QEMU passes the vmgenid/UUID via
fw_cfg to an intermediate UEFI firmware. This UEFI firmware, running as
a guest in QEMU, reads the UUID from fw_cfg and creates ACPI tables for
it. The UEFI firmware then passes the UUID information to the guest
kernel via ACPI.
This approach requires yet another intermediary which is UEFI firmware
and adds more complexity than ACPI for minimalist hypervisors that do
not have an intermediate bootloader today.
Rob
[1] https://www.kernel.org/doc/Documentation/devicetree/bindings/firmware/qemu%2Cfw-cfg-mmio.yaml
