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 <[email protected]>
Acked-by: Baoquan He <[email protected]>
---
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;
+ }
+ }
+ unmap_crash_pages((void **)&ptr);
+ }
+ }
+
if (!image->elfcorehdr_index_valid) {
pr_err("crash hp: unable to locate elfcorehdr segment");
goto out;
--
2.27.0
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 <[email protected]>
> Acked-by: Baoquan He <[email protected]>
> ---
> 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
On 5/25/22 09:26, Sourabh Jain wrote:
> 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 <[email protected]>
>> Acked-by: Baoquan He <[email protected]>
>> ---
>> 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.
That would be a viable place to put it. However, a couple of notes.
This code actually works for both kexec_load and kexec_file_load paths (how I originally used this
code); so if we were to move this to a more common location, I'd be in favor of a location that
serves both paths (ie handle_hotplug_event() makes sense to me). That would eliminate the need for
setting the index in the kexec_file_load paths.
Also, I don't see a scenario where elfcorehdr_index_valid can be eliminated; the index isn't always
valid. What are you thinking?
And the check is rather low cost being the check of a boolean.
eric
>
> Thanks,
> Sourabh Jain
>
>