[PATCH v18 00/15] arm64: MMU enabled kexec relocation

From: Pasha Tatashin
Date: Thu Sep 30 2021 - 10:31:19 EST

Changelog:
v18:
- Addressed comments from Will Deacon
- Added Acks from Catalin Marinas
v17:
- Merged with 5.15-rc1 as requested by Catalin Marinas
- Added Tested-by: Pingfan Liu <piliu@xxxxxxxxxx>
v16:
- Merged with 5.14-rc4
v15:
- Changed trans_pgd_copy_el2_vectors() to use vector table that
only shared by kexec and hibernate. This way sync does not have
dangling branch that was recently introduced. (Reported by Marc
Zyngier)
- Renamed is_hyp_callable() to is_hyp_nvhe() as requested by Marc
Zyngier
- Clean-ups, comment fixes.
- Sync with upstream 368094df48e680fa51cedb68537408cfa64b788e
v14:
- Fixed a bug in "arm64: hyp-stub: Move elx_sync into the vectors"
that was noticed by Marc Zyngier
- Merged with upstream
v13:
- Fixed a hang on ThunderX2, thank you Pingfan Liu for reporting
the problem. In relocation function we need civac not ivac, we
need to clean data in addition to invalidating it.
Since I was using ThunderX2 machine I also measured the new
performance data on this large ARM64 server. The MMU improves
kexec relocation 190 times on this machine! (see below for
raw data). Saves 7.5s during CentOS kexec reboot.
v12:
- A major change compared to previous version. Instead of using
contiguous VA range a copy of linear map is now used to perform
copying of segments during relocation as it was agreed in the
discussion of version 11 of this project.
- In addition to using linear map, I also took several ideas from
James Morse to better organize the kexec relocation:
1. skip relocation function entirely if that is not needed
2. remove the PoC flushing function since it is not needed
anymore with MMU enabled.
v11:
- Fixed missing KEXEC_CORE dependency for trans_pgd.c
- Removed useless "if(rc) return rc" statement (thank you Tyler Hicks)
- Another 12 patches were accepted into maintainer's get.
Re-based patches against:
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
Branch: for-next/kexec
v10:
- Addressed a lot of comments form James Morse and from Marc Zyngier
- Added review-by's
- Synchronized with mainline

v9: - 9 patches from previous series landed in upstream, so now series
is smaller
- Added two patches from James Morse to address idmap issues for machines
with high physical addresses.
- Addressed comments from Selin Dag about compiling issues. He also tested
my series and got similar performance results: ~60 ms instead of ~580 ms
with an initramfs size of ~120MB.
v8:
- Synced with mainline to keep series up-to-date
v7:
-- Addressed comments from James Morse
- arm64: hibernate: pass the allocated pgdp to ttbr0
Removed "Fixes" tag, and added Added Reviewed-by: James Morse
- arm64: hibernate: check pgd table allocation
Sent out as a standalone patch so it can be sent to stable
Series applies on mainline + this patch
- arm64: hibernate: add trans_pgd public functions
Remove second allocation of tmp_pg_dir in swsusp_arch_resume
Added Reviewed-by: James Morse <james.morse@xxxxxxx>
- arm64: kexec: move relocation function setup and clean up
Fixed typo in commit log
Changed kern_reloc to phys_addr_t types.
Added explanation why kern_reloc is needed.
Split into four patches:
arm64: kexec: make dtb_mem always enabled
arm64: kexec: remove unnecessary debug prints
arm64: kexec: call kexec_image_info only once
arm64: kexec: move relocation function setup
- arm64: kexec: add expandable argument to relocation function
Changed types of new arguments from unsigned long to phys_addr_t.
Changed offset prefix to KEXEC_*
Split into four patches:
arm64: kexec: cpu_soft_restart change argument types
arm64: kexec: arm64_relocate_new_kernel clean-ups
arm64: kexec: arm64_relocate_new_kernel don't use x0 as temp
arm64: kexec: add expandable argument to relocation function
- arm64: kexec: configure trans_pgd page table for kexec
Added invalid entries into EL2 vector table
Removed KEXEC_EL2_VECTOR_TABLE_SIZE and KEXEC_EL2_VECTOR_TABLE_OFFSET
Copy relocation functions and table into separate pages
Changed types in kern_reloc_arg.
Split into three patches:
arm64: kexec: offset for relocation function
arm64: kexec: kexec EL2 vectors
arm64: kexec: configure trans_pgd page table for kexec
- arm64: kexec: enable MMU during kexec relocation
Split into two patches:
arm64: kexec: enable MMU during kexec relocation
arm64: kexec: remove head from relocation argument
v6:
- Sync with mainline tip
- Added Acked's from Dave Young
v5:
- Addressed comments from Matthias Brugger: added review-by's, improved
comments, and made cleanups to swsusp_arch_resume() in addition to
create_safe_exec_page().
- Synced with mainline tip.
v4:
- Addressed comments from James Morse.
- Split "check pgd table allocation" into two patches, and moved to
the beginning of series for simpler backport of the fixes.
Added "Fixes:" tags to commit logs.
- Changed "arm64, hibernate:" to "arm64: hibernate:"
- Added Reviewed-by's
- Moved "add PUD_SECT_RDONLY" earlier in series to be with other
clean-ups
- Added "Derived from:" to arch/arm64/mm/trans_pgd.c
- Removed "flags" from trans_info
- Changed .trans_alloc_page assumption to return zeroed page.
- Simplify changes to trans_pgd_map_page(), by keeping the old
code.
- Simplify changes to trans_pgd_create_copy, by keeping the old
code.
- Removed: "add trans_pgd_create_empty"
- replace init_mm with NULL, and keep using non "__" version of
populate functions.
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
----------------

Cavium ThunderX2:
Kernel Image size: 38M Iniramfs size: 46M Total relocation size: 84M
MMU-disabled:
relocation 7.489539915s
MMU-enabled:
relocation 0.03946095s

Relocation performance is improved 190 times.

Broadcom Stingray:
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.

MMU-disabled::
kernel shutdown 0.022131328s
relocation 0.440510736s
kernel startup 0.294706768s

Relocation was taking: 58.2% of reboot time

MMU-enabled:
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
-----------------------------------
v17: https://lore.kernel.org/lkml/20210916231325.125533-1-pasha.tatashin@xxxxxxxxxx
v16: https://lore.kernel.org/lkml/20210802215408.804942-1-pasha.tatashin@xxxxxxxxxx
v15: https://lore.kernel.org/lkml/20210609004419.936873-1-pasha.tatashin@xxxxxxxxxx
v14: https://lore.kernel.org/lkml/20210527150526.271941-1-pasha.tatashin@xxxxxxxxxx
v13: https://lore.kernel.org/lkml/20210408040537.2703241-1-pasha.tatashin@xxxxxxxxxx
v12: https://lore.kernel.org/lkml/20210303002230.1083176-1-pasha.tatashin@xxxxxxxxxx
v11: https://lore.kernel.org/lkml/20210127172706.617195-1-pasha.tatashin@xxxxxxxxxx
v10: https://lore.kernel.org/linux-arm-kernel/20210125191923.1060122-1-pasha.tatashin@xxxxxxxxxx
v9: https://lore.kernel.org/lkml/20200326032420.27220-1-pasha.tatashin@xxxxxxxxxx
v8: https://lore.kernel.org/lkml/20191204155938.2279686-1-pasha.tatashin@xxxxxxxxxx
v7: https://lore.kernel.org/lkml/20191016200034.1342308-1-pasha.tatashin@xxxxxxxxxx
v6: https://lore.kernel.org/lkml/20191004185234.31471-1-pasha.tatashin@xxxxxxxxxx
v5: https://lore.kernel.org/lkml/20190923203427.294286-1-pasha.tatashin@xxxxxxxxxx
v4: https://lore.kernel.org/lkml/20190909181221.309510-1-pasha.tatashin@xxxxxxxxxx
v3: https://lore.kernel.org/lkml/20190821183204.23576-1-pasha.tatashin@xxxxxxxxxx
v2: https://lore.kernel.org/lkml/20190817024629.26611-1-pasha.tatashin@xxxxxxxxxx
v1: https://lore.kernel.org/lkml/20190801152439.11363-1-pasha.tatashin@xxxxxxxxxx

Pasha Tatashin (15):
arm64: kernel: add helper for booted at EL2 and not VHE
arm64: trans_pgd: hibernate: Add trans_pgd_copy_el2_vectors
arm64: hibernate: abstract ttrb0 setup function
arm64: kexec: flush image and lists during kexec load time
arm64: kexec: skip relocation code for inplace kexec
arm64: kexec: Use dcache ops macros instead of open-coding
arm64: kexec: pass kimage as the only argument to relocation function
arm64: kexec: configure EL2 vectors for kexec
arm64: kexec: relocate in EL1 mode
arm64: kexec: use ld script for relocation function
arm64: kexec: install a copy of the linear-map
arm64: kexec: keep MMU enabled during kexec relocation
arm64: kexec: remove the pre-kexec PoC maintenance
arm64: kexec: remove cpu-reset.h
arm64: trans_pgd: remove trans_pgd_map_page()

arch/arm64/Kconfig | 2 +-
arch/arm64/include/asm/assembler.h | 49 ++++++--
arch/arm64/include/asm/kexec.h | 12 ++
arch/arm64/include/asm/mmu_context.h | 24 ++++
arch/arm64/include/asm/sections.h | 1 +
arch/arm64/include/asm/trans_pgd.h | 14 ++-
arch/arm64/include/asm/virt.h | 7 ++
arch/arm64/kernel/asm-offsets.c | 11 ++
arch/arm64/kernel/cpu-reset.S | 7 +-
arch/arm64/kernel/cpu-reset.h | 32 -----
arch/arm64/kernel/hibernate-asm.S | 72 -----------
arch/arm64/kernel/hibernate.c | 49 ++------
arch/arm64/kernel/machine_kexec.c | 177 ++++++++++++++-------------
arch/arm64/kernel/relocate_kernel.S | 69 +++++------
arch/arm64/kernel/sdei.c | 2 +-
arch/arm64/kernel/vmlinux.lds.S | 19 +++
arch/arm64/mm/Makefile | 1 +
arch/arm64/mm/trans_pgd-asm.S | 65 ++++++++++
arch/arm64/mm/trans_pgd.c | 84 ++++---------
19 files changed, 357 insertions(+), 340 deletions(-)
delete mode 100644 arch/arm64/kernel/cpu-reset.h
create mode 100644 arch/arm64/mm/trans_pgd-asm.S

--
2.33.0.800.g4c38ced690-goog