[v3,00/17] arm64: MMU enabled kexec relocation

Message

Pasha Tatashin Aug. 21, 2019, 6:31 p.m. UTC

Changelog:
v3:
	- Split changes to create_safe_exec_page() into several patches for
	  easier review as request by Mark Rutland. This is why this series
	  has 3 more patches.
	- Renamed trans_table to tans_pgd as agreed with Mark. The header
	  comment in trans_pgd.c explains that trans stands for
	  transitional page tables. Meaning they are used in transition
	  between two kernels.
v2:
	- Fixed hibernate bug reported by James Morse
	- Addressed comments from James Morse:
	  * More incremental changes to trans_table
	  * Removed TRANS_FORCEMAP
	  * Added kexec reboot data for image with 380M in size.

Enable MMU during kexec relocation in order to improve reboot performance.

If kexec functionality is used for a fast system update, with a minimal
downtime, the relocation of kernel + initramfs takes a significant portion
of reboot.

The reason for slow relocation is because it is done without MMU, and thus
not benefiting from D-Cache.

Performance data
----------------
For this experiment, the size of kernel plus initramfs is small, only 25M.
If initramfs was larger, than the improvements would be greater, as time
spent in relocation is proportional to the size of relocation.

Previously:
kernel shutdown	0.022131328s
relocation	0.440510736s
kernel startup	0.294706768s

Relocation was taking: 58.2% of reboot time

Now:
kernel shutdown	0.032066576s
relocation	0.022158152s
kernel startup	0.296055880s

Now: Relocation takes 6.3% of reboot time

Total reboot is x2.16 times faster.

With bigger userland (fitImage 380M), the reboot time is improved by 3.57s,
and is reduced from 3.9s down to 0.33s

Previous approaches and discussions
-----------------------------------
https://lore.kernel.org/lkml/[e-mail]
version 2 of this series

https://lore.kernel.org/lkml/[e-mail]
version 1 of this series

https://lore.kernel.org/lkml/[e-mail]
reserve space for kexec to avoid relocation, involves changes to generic code
to optimize a problem that exists on arm64 only:

https://lore.kernel.org/lkml/[e-mail]
The first attempt to enable MMU, some bugs that prevented performance
improvement. The page tables unnecessary configured idmap for the whole
physical space.

https://lore.kernel.org/lkml/[e-mail]
No linear copy, bug with EL2 reboots.

Pavel Tatashin (17):
  kexec: quiet down kexec reboot
  arm64, hibernate: use get_safe_page directly
  arm64, hibernate: remove gotos in create_safe_exec_page
  arm64, hibernate: rename dst to page in create_safe_exec_page
  arm64, hibernate: check pgd table allocation
  arm64, hibernate: add trans_pgd public functions
  arm64, hibernate: move page handling function to new trans_pgd.c
  arm64, trans_pgd: make trans_pgd_map_page generic
  arm64, trans_pgd: add trans_pgd_create_empty
  arm64, trans_pgd: adjust trans_pgd_create_copy interface
  arm64, trans_pgd: add PUD_SECT_RDONLY
  arm64, trans_pgd: complete generalization of trans_pgds
  kexec: add machine_kexec_post_load()
  arm64, kexec: move relocation function setup and clean up
  arm64, kexec: add expandable argument to relocation function
  arm64, kexec: configure trans_pgd page table for kexec
  arm64, kexec: enable MMU during kexec relocation

 arch/arm64/Kconfig                     |   4 +
 arch/arm64/include/asm/kexec.h         |  51 ++++-
 arch/arm64/include/asm/pgtable-hwdef.h |   1 +
 arch/arm64/include/asm/trans_pgd.h     |  63 ++++++
 arch/arm64/kernel/asm-offsets.c        |  14 ++
 arch/arm64/kernel/cpu-reset.S          |   4 +-
 arch/arm64/kernel/cpu-reset.h          |   8 +-
 arch/arm64/kernel/hibernate.c          | 261 ++++++------------------
 arch/arm64/kernel/machine_kexec.c      | 199 ++++++++++++++----
 arch/arm64/kernel/relocate_kernel.S    | 196 +++++++++---------
 arch/arm64/mm/Makefile                 |   1 +
 arch/arm64/mm/trans_pgd.c              | 270 +++++++++++++++++++++++++
 kernel/kexec.c                         |   4 +
 kernel/kexec_core.c                    |   8 +-
 kernel/kexec_file.c                    |   4 +
 kernel/kexec_internal.h                |   2 +
 16 files changed, 750 insertions(+), 340 deletions(-)
 create mode 100644 arch/arm64/include/asm/trans_pgd.h
 create mode 100644 arch/arm64/mm/trans_pgd.c