Re: [PATCH v4 05/14] kexec: Add Kexec HandOver (KHO) generation helpers

["Thomas Weißschuh" <linux@weissschuh.net>]

On 2025-02-06 15:27:45+0200, Mike Rapoport wrote:
> From: Alexander Graf <graf@amazon.com>
> 
> This patch adds the core infrastructure to generate Kexec HandOver
> metadata. Kexec HandOver is a mechanism that allows Linux to preserve
> state - arbitrary properties as well as memory locations - across kexec.
> 
> It does so using 2 concepts:
> 
>   1) Device Tree - Every KHO kexec carries a KHO specific flattened
>      device tree blob that describes the state of the system. Device
>      drivers can register to KHO to serialize their state before kexec.
> 
>   2) Scratch Regions - CMA regions that we allocate in the first kernel.
>      CMA gives us the guarantee that no handover pages land in those
>      regions, because handover pages must be at a static physical memory
>      location. We use these regions as the place to load future kexec
>      images so that they won't collide with any handover data.
> 
> Signed-off-by: Alexander Graf <graf@amazon.com>
> Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  Documentation/ABI/testing/sysfs-kernel-kho    |  53 +++
>  .../admin-guide/kernel-parameters.txt         |  24 +
>  MAINTAINERS                                   |   1 +
>  include/linux/cma.h                           |   2 +
>  include/linux/kexec.h                         |  18 +
>  include/linux/kexec_handover.h                |  10 +
>  kernel/Makefile                               |   1 +
>  kernel/kexec_handover.c                       | 450 ++++++++++++++++++
>  mm/internal.h                                 |   3 -
>  mm/mm_init.c                                  |   8 +
>  10 files changed, 567 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-kernel-kho
>  create mode 100644 include/linux/kexec_handover.h
>  create mode 100644 kernel/kexec_handover.c

<snip>

> --- /dev/null
> +++ b/include/linux/kexec_handover.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef LINUX_KEXEC_HANDOVER_H
> +#define LINUX_KEXEC_HANDOVER_H

#include <linux/types.h>

> +
> +struct kho_mem {
> +	phys_addr_t addr;
> +	phys_addr_t size;
> +};
> +
> +#endif /* LINUX_KEXEC_HANDOVER_H */

<snip>

> +static ssize_t dt_read(struct file *file, struct kobject *kobj,
> +		       struct bin_attribute *attr, char *buf,

Please make the bin_attribute argument const. Currently both work, but
the non-const variant will go away.
This way I can test my stuff on linux-next.

> +		       loff_t pos, size_t count)
> +{
> +	mutex_lock(&kho_out.lock);
> +	memcpy(buf, attr->private + pos, count);
> +	mutex_unlock(&kho_out.lock);
> +
> +	return count;
> +}
> +
> +struct bin_attribute bin_attr_dt_kern = __BIN_ATTR(dt, 0400, dt_read, NULL, 0);

The new __BIN_ATTR_ADMIN_RO() could make this slightly shorter.

<snip>