Re: [PATCH v8 7/7] x86/crash: Add x86 crash hotplug support for kexec_load

Sourabh Jain
2022-05-25T14:29:13Z

Hello Eric,

On 06/05/22 00:16, Eric DeVolder wrote:
> For kexec_file_load support, the loading of the crash kernel occurs
> entirely within the kernel, and as such the elfcorehdr is readily
> identified (so that it can be modified upon hotplug events).
>
> This change enables support for kexec_load by identifying the
> elfcorehdr segment in the arch_crash_handle_hotplug_event(),
> if it has not already been identified.
>
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> Acked-by: Baoquan He <bhe@redhat.com>
> ---
> arch/x86/kernel/crash.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 951ef365f0a7..845d7c77854d 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -485,6 +485,30 @@ void arch_crash_handle_hotplug_event(struct kimage *image,
> void *elfbuf = NULL;
> unsigned long mem, memsz;
>
> + /*
> + * When the struct kimage is alloced, it is wiped to zero, so
> + * the elfcorehdr_index_valid defaults to false. It is set on the
> + * kexec_file_load path, or here for kexec_load, if not already
> + * identified.
> + */
> + if (!image->elfcorehdr_index_valid) {
> + unsigned int n;
> +
> + for (n = 0; n < image->nr_segments; n++) {
> + mem = image->segment[n].mem;
> + memsz = image->segment[n].memsz;
> + ptr = map_crash_pages(mem, memsz);
> + if (ptr) {
> + /* The segment containing elfcorehdr */
> + if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> + image->elfcorehdr_index = (int)n;
> + image->elfcorehdr_index_valid = true;

How about finding elfcorehdr index on kexec_load path post
kimage_load_segment call in
do_kexec_load (kernel/kexec.c) or other suitable place? This way we can
avoid checking for
elfcorehdr index for every hotplug. Also we might not need
image->elfcorehdr_index_valid.

Thanks,
Sourabh Jain