by Pingfan Liu

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Subject: Re: [PATCH v12 00/17] arm64: MMU enabled kexec relocation

Hi Pavel,

After going through this series, I think if this can be done by using
identity map through ttbr0.

Then the processes may be neat (I hope so):
-1. set up identity map in machine_kexec_post_load(), instead of
copying linear map.
-2. Also past this temporary identity map to arm64_relocate_new_kernel()
-3. in arm64_relocate_new_kernel(), just load identity map and
re-enable MMU. After copying, just turn off MMU.

Thanks,
Pingfan

On Thu, Mar 4, 2021 at 3:47 PM Pavel Tatashin <[email protected]> wrote:
>
> Changelog:
> 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 <[email protected]>
> - 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
> ----------------
> 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
> -----------------------------------
> v11: https://lore.kernel.org/lkml/[email protected]
> v10: https://lore.kernel.org/linux-arm-kernel/[email protected]
> v9: https://lore.kernel.org/lkml/[email protected]
> v8: https://lore.kernel.org/lkml/[email protected]
> v7: https://lore.kernel.org/lkml/[email protected]
> v6: https://lore.kernel.org/lkml/[email protected]
> v5: https://lore.kernel.org/lkml/[email protected]
> v4: https://lore.kernel.org/lkml/[email protected]
> v3: https://lore.kernel.org/lkml/[email protected]
> v2: https://lore.kernel.org/lkml/[email protected]
> v1: https://lore.kernel.org/lkml/[email protected]
>
> James Morse (4):
> arm64: hyp-stub: Check the size of the HYP stub's vectors
> arm64: hyp-stub: Move invalid vector entries into the vectors
> arm64: hyp-stub: Move el1_sync into the vectors
> arm64: kexec: Use dcache ops macros instead of open-coding
>
> Pavel Tatashin (13):
> 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: pass kimage as the only argument to relocation function
> arm64: kexec: kexec may require EL2 vectors
> 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
>
> arch/arm64/Kconfig | 2 +-
> arch/arm64/include/asm/assembler.h | 31 ++++-
> 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 | 3 +
> arch/arm64/include/asm/virt.h | 8 ++
> 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 | 20 ----
> arch/arm64/kernel/hibernate.c | 56 +++------
> arch/arm64/kernel/hyp-stub.S | 95 +++++++--------
> arch/arm64/kernel/machine_kexec.c | 168 +++++++++++++++------------
> arch/arm64/kernel/relocate_kernel.S | 72 ++++++------
> arch/arm64/kernel/sdei.c | 2 +-
> arch/arm64/kernel/vmlinux.lds.S | 19 +++
> arch/arm64/mm/trans_pgd.c | 20 ++++
> 18 files changed, 314 insertions(+), 269 deletions(-)
> delete mode 100644 arch/arm64/kernel/cpu-reset.h
>
> --
> 2.25.1
>