Re: [PATCH v2 1/2] kexec: history: track previous kernel version

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Fri, Jan 2, 2026 at 9:53 AM Breno Leitao <leitao@debian.org> wrote:
>
> Add CONFIG_KEXEC_HISTORY to store and display the kernel version from
> the previous kexec boot.

I do not think we need a config. Let's just enable this by default, as
I suggested in RFC.

>
> When enabled, the current kernel's release string is saved to the
> "previous-release" property in the KHO device tree before kexec. On
> the next boot, if this property exists, the previous kernel version
> is retrieved and printed during early boot.
>
> This helps diagnose bugs that only manifest when kexecing from
> specific kernel versions, making it easier to correlate crashes with
> the kernel that initiated the kexec.
>
> Disabled by default to avoid overhead for users who don't need this
> information.
>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  kernel/Kconfig.kexec               | 13 +++++++++++++
>  kernel/liveupdate/kexec_handover.c | 29 +++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
>
> diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec
> index 15632358bcf7..b770c68a3800 100644
> --- a/kernel/Kconfig.kexec
> +++ b/kernel/Kconfig.kexec
> @@ -94,6 +94,19 @@ config KEXEC_JUMP
>           Jump between original kernel and kexeced kernel and invoke
>           code in physical address mode via KEXEC
>
> +config KEXEC_HISTORY
> +       bool "Track kexec kernel history"
> +       depends on KEXEC_HANDOVER
> +       help
> +         When enabled, the kernel will store its release version in the
> +         KHO FDT before kexec, and the newly booted kernel will read and
> +         print this information during early boot.
> +
> +         This is useful for debugging and auditing to know which kernel
> +         version performed the kexec that booted the current kernel.
> +
> +         If unsure, say N.
> +
>  config CRASH_DUMP
>         bool "kernel crash dumps"
>         default ARCH_DEFAULT_CRASH_DUMP
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 73da00aeaa99..06d99627bb3c 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -21,6 +21,7 @@
>  #include <linux/page-isolation.h>
>  #include <linux/unaligned.h>
>  #include <linux/vmalloc.h>
> +#include <linux/utsname.h>
>
>  #include <asm/early_ioremap.h>
>
> @@ -36,6 +37,7 @@
>  #define KHO_FDT_COMPATIBLE "kho-v1"
>  #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
>  #define PROP_SUB_FDT "fdt"
> +#define PROP_PREVIOUS_RELEASE "previous-release"
>
>  #define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */
>
> @@ -1253,6 +1255,9 @@ bool kho_finalized(void)
>  struct kho_in {
>         phys_addr_t fdt_phys;
>         phys_addr_t scratch_phys;
> +#ifdef CONFIG_KEXEC_HISTORY
> +       char previous_release[__NEW_UTS_LEN + 1];
> +#endif
>         struct kho_debugfs dbg;
>  };
>
> @@ -1332,6 +1337,10 @@ static __init int kho_out_fdt_setup(void)
>         err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE);
>         err |= fdt_property(root, PROP_PRESERVED_MEMORY_MAP, &empty_mem_map,
>                             sizeof(empty_mem_map));
> +#ifdef CONFIG_KEXEC_HISTORY
> +       err |= fdt_property_string(root, PROP_PREVIOUS_RELEASE,
> +                                  init_uts_ns.name.release);
> +#endif
>         err |= fdt_end_node(root);
>         err |= fdt_finish(root);
>
> @@ -1455,6 +1464,25 @@ void __init kho_memory_init(void)
>         }
>  }
>
> +#ifdef CONFIG_KEXEC_HISTORY
> +static void __init kho_print_previous_kernel(const void *fdt)
> +{
> +       const char *prev_release;
> +       int len;
> +
> +       prev_release = fdt_getprop(fdt, 0, PROP_PREVIOUS_RELEASE, &len);
> +       if (!prev_release || len <= 0)
> +               return;
> +
> +       strscpy(kho_in.previous_release, prev_release,
> +               sizeof(kho_in.previous_release));
> +       pr_info("This kernel was kexec'ed from kernel release: %s\n",
> +               kho_in.previous_release);

May be reduce the message slightly:
i.e. "kexec from: %s\n, kho_in.previous_release"

> +}
> +#else
> +static void __init kho_print_previous_kernel(const void *fdt) { }
> +#endif
> +
>  void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
>                          phys_addr_t scratch_phys, u64 scratch_len)
>  {
> @@ -1527,6 +1555,7 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
>         kho_in.scratch_phys = scratch_phys;
>         kho_scratch_cnt = scratch_cnt;
>         pr_info("found kexec handover data.\n");

This message is not needed if the previous kernel version is always printed.

> +       kho_print_previous_kernel(fdt);
>
>  out:
>         if (fdt)
>
> --
> 2.47.3
>