On Fri, Jan 2, 2026 at 9:53 AM Breno Leitao <[email protected]> wrote:
>
> Track and display the number of kexec boots since the last cold reboot
> when CONFIG_KEXEC_HISTORY is enabled.
>
> This extends the previous kernel release tracking feature by adding
> a counter that increments with each kexec boot. The counter provides
> visibility into the kexec chain depth, which is useful for understanding
> boot history in production environments.
>
> Add a new property, "kexec-count" in KHO FDT alongside the existing
> "previous-release" property. The counter is:
>
> - Initialized to 0 when kho_in is instantiated.
> - Incremented by 1 on each subsequent kexec.
> - Printed alongside the previous kernel release version.
>
> The counter is stored as a 32-bit unsigned integer in FDT format and is
> only active when CONFIG_KEXEC_HISTORY is enabled.
>
> Signed-off-by: Breno Leitao <[email protected]>
> Suggested-by: Pasha Tatashin <[email protected]>
> ---
> kernel/liveupdate/kexec_handover.c | 25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> index 06d99627bb3c..fe5a2c5c4c86 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -38,6 +38,7 @@
> #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
> #define PROP_SUB_FDT "fdt"
> #define PROP_PREVIOUS_RELEASE "previous-release"
> +#define PROP_KEXEC_COUNT "kexec-count"
>
> #define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */
>
> @@ -1257,6 +1258,7 @@ struct kho_in {
> phys_addr_t scratch_phys;
> #ifdef CONFIG_KEXEC_HISTORY
> char previous_release[__NEW_UTS_LEN + 1];
> + u32 kexec_count;
> #endif
> struct kho_debugfs dbg;
> };
> @@ -1330,6 +1332,9 @@ static __init int kho_out_fdt_setup(void)
> void *root = kho_out.fdt;
> u64 empty_mem_map = 0;
> int err;
> +#ifdef CONFIG_KEXEC_HISTORY
> + u32 kexec_count;
> +#endif
>
> err = fdt_create(root, PAGE_SIZE);
> err |= fdt_finish_reservemap(root);
> @@ -1340,6 +1345,10 @@ static __init int kho_out_fdt_setup(void)
> #ifdef CONFIG_KEXEC_HISTORY
> err |= fdt_property_string(root, PROP_PREVIOUS_RELEASE,
> init_uts_ns.name.release);
> + /* kho_in.kexec_count is set to 0 on cold boot */
> + kexec_count = cpu_to_fdt32(kho_in.kexec_count + 1);
For KHO preserved data we use native endiness, so do not bother with
cpu_to_fdt32.
> + err |= fdt_property(root, PROP_KEXEC_COUNT, &kexec_count,
> + sizeof(kexec_count));
> #endif
> err |= fdt_end_node(root);
> err |= fdt_finish(root);
> @@ -1468,6 +1477,7 @@ void __init kho_memory_init(void)
> static void __init kho_print_previous_kernel(const void *fdt)
> {
> const char *prev_release;
> + const u32 *count_ptr;
> int len;
>
> prev_release = fdt_getprop(fdt, 0, PROP_PREVIOUS_RELEASE, &len);
> @@ -1476,8 +1486,19 @@ static void __init kho_print_previous_kernel(const
> void *fdt)
>
> 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);
> +
> + /* Read the kexec count from the previous kernel */
> + count_ptr = fdt_getprop(fdt, 0, PROP_KEXEC_COUNT, &len);
> + if (WARN_ON_ONCE(!count_ptr || len <= 0))
This function is called only once anway.
> + /*
> + * PROP_KEXEC_COUNT should exist if PROP_PREVIOUS_RELEASE
> + * exists.
> + */
> + return;
> + kho_in.kexec_count = fdt32_to_cpu(*count_ptr);
> +
> + pr_info("This kernel was kexec'ed from kernel release: %s (kexec
> count: %u)\n",
> + kho_in.previous_release, kho_in.kexec_count);
> }
> #else
> static void __init kho_print_previous_kernel(const void *fdt) { }
>
> --
> 2.47.3
>
