[v2 0/5] arm64: allow to reserve memory for normal kexec kernel
matthias.bgg at gmail.com
Wed Jul 10 08:28:34 PDT 2019
On 09/07/2019 20:20, Pavel Tatashin wrote:
> v1 - v2
> - No changes to patches, addressed suggestion from James Morse
> to add "arm64" tag to cover letter.
> - Improved cover letter information based on discussion.
> Currently, it is only allowed to reserve memory for crash kernel, because
> it is a requirement in order to be able to boot into crash kernel without
> touching memory of crashed kernel is to have memory reserved.
> The second benefit for having memory reserved for kexec kernel is
> that it does not require a relocation after segments are loaded into
> If kexec functionality is used for a fast system update, with a minimal
> downtime, the relocation of kernel + initramfs might take a significant
> portion of reboot.
> In fact, on the machine that we are using, that has ARM64 processor
> it takes 0.35s to relocate during kexec, thus taking 52% of kernel reboot
> kernel shutdown 0.03s
> relocation 0.35s
> kernel startup 0.29s
> Image: 13M and initramfs is 24M. If initramfs increases, the relocation
> time increases proportionally.
> While, it is possible to add 'kexeckernel=' parameters support to other
> architectures by modifying reserve_crashkernel(), in this series this is
> done for arm64 only.
I wonder if we couldn't use the crashkernel reserved memory area for that and
just add logic to kexec-tools to pass to the kernel a flag (a new magic reboot
number?) to use the crashkernel memory for that?
The kernel would then unload the crash/capture system in the reserved memory
area and reuse the latter for kexec.
This would also enable the feature for all architectures.
> The reason it is so slow on arm64 to relocate kernel is because the code
> that does relocation does this with MMU disabled, and thus D-Cache and
> I-Cache must also be disabled.
> Alternative solution is more complicated: Setup a temporary page table
> for relocation_routine and also for code from cpu_soft_restart. Perform
> relocation with MMU enabled, do cpu_soft_restart where MMU and caching
> are disabled, jump to purgatory. A similar approach was suggested for
> purgatory and was rejected due to making purgatory too complicated.
> On, the other hand hibernate does something similar already, but there
> MMU never needs to be disabled, and also by the time machine_kexec()
> is called, allocator is not available, as we can't fail to do reboot,
> so page table must be pre-allocated during kernel load time.
> Note: the above time is relocation time only. Purgatory usually also
> computes checksum, but that is skipped, because --no-check is used when
> kernel image is loaded via kexec.
> Pavel Tatashin (5):
> kexec: quiet down kexec reboot
> kexec: add resource for normal kexec region
> kexec: export common crashkernel/kexeckernel parser
> kexec: use reserved memory for normal kexec reboot
> arm64, kexec: reserve kexeckernel region
> .../admin-guide/kernel-parameters.txt | 7 ++
> arch/arm64/kernel/setup.c | 5 ++
> arch/arm64/mm/init.c | 83 ++++++++++++-------
> include/linux/crash_core.h | 6 ++
> include/linux/ioport.h | 1 +
> include/linux/kexec.h | 6 +-
> kernel/crash_core.c | 27 +++---
> kernel/kexec_core.c | 50 +++++++----
> 8 files changed, 127 insertions(+), 58 deletions(-)
More information about the kexec