[PATCH 2/2] kexec_file: Load kernel at top of system RAM if required

Baoquan He bhe at redhat.com
Tue Nov 14 20:16:58 AEDT 2023

Kexec_load interface has been doing top down searching and loading
kernel/initrd/purgtory etc to prepare for kexec reboot. In that way,
the benefits are that it avoids to consume and fragment limited low
memory which satisfy DMA buffer allocation and big chunk of continuous
memory during system init; and avoids to stir with BIOS/FW reserved
or occupied areas, or corner case handling/work around/quirk occupied
areas when doing system init. By the way, the top-down searching and
loading of kexec-ed kernel is done in user space utility code.

For kexec_file loading, even if kexec_buf.top_down is 'true', it's simply
ignored. It calls walk_system_ram_res() directly to go through all
resources of System RAM bottom up, to find an available memory region,
then call locate_mem_hole_callback() to allocate memory in that found
memory region from top to down. This is not expected and inconsistent
with kexec_load.

Here check if kexec_buf.top_down is 'true' in kexec_walk_resources(),
if yes, call the newly added walk_system_ram_res_rev() to find memory
region of system RAM from top to down to load kernel/initrd etc.

Signed-off-by: Baoquan He <bhe at redhat.com>
 kernel/kexec_file.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index f9a419cd22d4..ba3ef30921b8 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -592,6 +592,8 @@ static int kexec_walk_resources(struct kexec_buf *kbuf,
 					   crashk_res.start, crashk_res.end,
 					   kbuf, func);
+	else if (kbuf->top_down)
+		return walk_system_ram_res_rev(0, ULONG_MAX, kbuf, func);
 		return walk_system_ram_res(0, ULONG_MAX, kbuf, func);

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