Re: [PATCH v8 17/17] Documentation: KHO: Add memblock bindings

Ricardo Neri
2025-12-11T02:53:21Z

On Fri, May 09, 2025 at 12:46:35AM -0700, Changyuan Lyu wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
> We introduced KHO into Linux: A framework that allows Linux to pass
> metadata and memory across kexec from Linux to Linux. KHO reuses fdt
> as file format and shares a lot of the same properties of firmware-to-
> Linux boot formats: It needs a stable, documented ABI that allows for
> forward and backward compatibility as well as versioning.
>
> As first user of KHO, we introduced memblock which can now preserve
> memory ranges reserved with reserve_mem command line options contents
> across kexec, so you can use the post-kexec kernel to read traces from
> the pre-kexec kernel.
>
> This patch adds memblock schemas similar to "device" device tree ones to
> a new kho bindings directory. This allows us to force contributors to
> document the data that moves across KHO kexecs and catch breaking change
> during review.
>
> Co-developed-by: Alexander Graf <graf@amazon.com>
> Signed-off-by: Alexander Graf <graf@amazon.com>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Signed-off-by: Changyuan Lyu <changyuanl@google.com>
> ---
> .../kho/bindings/memblock/memblock.yaml | 39 ++++++++++++++++++
> .../kho/bindings/memblock/reserve-mem.yaml | 40 +++++++++++++++++++
> MAINTAINERS | 1 +
> 3 files changed, 80 insertions(+)
> create mode 100644 Documentation/core-api/kho/bindings/memblock/memblock.yaml
> create mode 100644 Documentation/core-api/kho/bindings/memblock/reserve-mem.yaml
>
> diff --git a/Documentation/core-api/kho/bindings/memblock/memblock.yaml b/Documentation/core-api/kho/bindings/memblock/memblock.yaml
> new file mode 100644
> index 0000000000000..d388c28eb91d1
> --- /dev/null
> +++ b/Documentation/core-api/kho/bindings/memblock/memblock.yaml
> @@ -0,0 +1,39 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +title: Memblock reserved memory
> +
> +maintainers:
> + - Mike Rapoport <rppt@kernel.org>
> +
> +description: |
> + Memblock can serialize its current memory reservations created with
> + reserve_mem command line option across kexec through KHO.
> + The post-KHO kernel can then consume these reservations and they are
> + guaranteed to have the same physical address.

Hi Changyuan, Mike,

I am sorry I am late to this patchset. I am working on a patchset to use
KHO to pass reserved memory regions to a driver after kexec and I have a
few questions.

> +
> +properties:
> + compatible:
> + enum:
> + - reserve-mem-v1

Shouldn't this be "memblock-v1". IIUC, the compatible "reserve-mem-v1" is
to be used for the memblock reserved memory regions, not the memblock node.

> +
> +patternProperties:
> + "$[0-9a-f_]+^":

Shouldn't this be "^[0-9a-f_]+$": ^ at the start of the pattern and $ at
the end of it? Or is this a KHO-specific rule?

Also, IIUC, this means that names of the nodes are hexadecimal numbers
whereas the example below has a "membloc" name. I assume this does not
refer to the subnode named "n1" as this does not follow the pattern
either Moreover, it should have been documented in the reserve-mem binding.

> + $ref: reserve-mem.yaml#
> + description: reserved memory regions
> +
> +required:
> + - compatible
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + memblock {
> + compatible = "memblock-v1";
> + n1 {
> + compatible = "reserve-mem-v1";
> + start = <0xc06b 0x4000000>;
> + size = <0x04 0x00>;
> + };
> + };

Thanks and BR,
Ricardo