Re: [PATCH v1 1/3] kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM_RAM resources

From: David Hildenbrand
Date: Tue Mar 23 2021 - 05:41:28 EST

On 22.03.21 17:01, David Hildenbrand wrote:
It used to be true that we can have busy system RAM only on the first level
in the resourc tree. However, this is no longer holds for driver-managed
system RAM (i.e., added via dax/kmem and virtio-mem), which gets added on
lower levels.

We have two users of walk_system_ram_res(), which currently only
consideres the first level:
a) kernel/kexec_file.c:kexec_walk_resources() -- We properly skip
locate_mem_hole_callback(), so even after this change, we won't be
placing kexec images onto dax/kmem and virtio-mem added memory. No
b) arch/x86/kernel/crash.c:fill_up_crash_elf_data() -- we're currently
not adding relevant ranges to the crash elf info, resulting in them
not getting dumped via kdump.

This change fixes loading a crashkernel via kexec_file_load() and including
dax/kmem and virtio-mem added System RAM in the crashdump on x86-64. Note
that e.g,, arm64 relies on memblock data and, therefore, always considers
all added System RAM already.

Let's find all busy IORESOURCE_SYSTEM_RAM resources, making the function
behave like walk_system_ram_range().

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
Cc: Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

^ My copy-paste action when creating the cc list slipped in a duplicate SO in all 3 patches. I can resend if desired.


David / dhildenb