[RFC 0/8] use __create_pgd_mapping() to implement idmap and unify codes

[Pingfan Liu]

Hi everyone,

Sorry to bring up this RFC in a hurry, since I paid attention to "arm64:
MMU enabled kexec relocation" too late and now it has advanced to "[PATCH
v13 00/18] arm64: MMU enabled kexec relocation".

And I think maybe that work can be based on my series.

I have raised my concern when reviewing "[PATCH v12 00/17] arm64: MMU
enabled kexec relocation"
  https://linuxlists.cc/l/1/linux-kernel/t/3923858/(patch_v12_00_17)_arm64:_mmu_enabled_kexec_relocation#post3948651
  (It seems that lore.kernel.org has not archived my reply)
  Where I wrote:
    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.

In a short discuss off-line, Pavel pointed to me
  https://lore.kernel.org/linux-arm-kernel/CA+CK2bC2KwWufE1DWa4szn_hQ1dbjDVHgYUu7=J4O_kvKXTrHg@mail.gmail.com/#t,
which prevent him from using idmap to implement his series.


After digging into the code, I find that if extending one more pgtable level,
the __create_pgd_mapping() routines can be re-used for idmap_pg_dir and
init_pg_dir. Besides, it can be re-used for trans_pgd_idmap_page().
That is what this series do.

As for "[PATCHv13 00/18] arm64: MMU enabled kexec relocation", here is
my two cents:
  -1. a call to create_idmap() API in machine_kexec_post_load(), to map
src + dst + arm64_relocate_new_kernel().
  -2. turn on MMU in arm64_relocate_new_kernel(), after done, turn off.

Sorry again for a hurry. It can be compiled, but far from good.

Thanks,

Pingfan

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Kristina Martsenko <kristina.martsenko at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Steven Price <steven.price at arm.com>
Cc: Jonathan Cameron <Jonathan.Cameron at huawei.com>
Cc: Pavel Tatashin <pasha.tatashin at soleen.com>
Cc: Anshuman Khandual <anshuman.khandual at arm.com>
Cc: Atish Patra <atish.patra at wdc.com>
Cc: Mike Rapoport <rppt at kernel.org>
Cc: Logan Gunthorpe <logang at deltatee.com>
Cc: Mark Brown <broonie at kernel.org>
To: linux-arm-kernel at lists.infradead.org

Pingfan Liu (8):
  arm64/mm: split out __create_pgd_mapping() routines
  arm64/mm: change __create_pgd_mapping() prototype to accept nr_entries
    and introduce create_idmap()
  arm64/mm: change __create_pgd_mapping() prototype to accept extra info
    for allocator
  arm64/mm: enable __create_pgd_mapping() to run across different
    pgtable
  arm64/mm: make trans_pgd_idmap_page() use create_idmap()
  arm64/mm: introduce pgtable allocator for head
  arm64/pgtable-prot.h: reorganize to cope with asm
  arm64/head: convert idmap_pg_dir and init_pg_dir to
    __create_pgd_mapping()

 arch/arm64/Kconfig                    |   4 +
 arch/arm64/include/asm/pgalloc.h      |  28 ++
 arch/arm64/include/asm/pgtable-prot.h |  34 ++-
 arch/arm64/kernel/head.S              | 190 ++++----------
 arch/arm64/mm/Makefile                |   2 +
 arch/arm64/mm/idmap_mmu.c             |  46 ++++
 arch/arm64/mm/mmu.c                   | 358 ++++++--------------------
 arch/arm64/mm/mmu_include.c           | 284 ++++++++++++++++++++
 arch/arm64/mm/trans_pgd.c             |  59 ++---
 9 files changed, 535 insertions(+), 470 deletions(-)
 create mode 100644 arch/arm64/mm/idmap_mmu.c
 create mode 100644 arch/arm64/mm/mmu_include.c

-- 
2.29.2