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[v4,0/5] Support Armv8.9/v9.4 FEAT_HAFT

Message ID 20241102104235.62560-1-yangyicong@huawei.com (mailing list archive)
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Series Support Armv8.9/v9.4 FEAT_HAFT | expand

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Yicong Yang Nov. 2, 2024, 10:42 a.m. UTC 
From: Yicong Yang <yangyicong@hisilicon.com>

This series adds basic support for FEAT_HAFT introduced in Armv8.9/v9.4
and enable ARCH_HAS_NONLEAF_PMD_YOUNG. The latter will be used in
lru-gen aging. Tested with lru-gen in below steps:
1. Generate a 1GiB workingset by `stress-ng --vm 1`. Then hang the task to
   stop accessing the memory. (AF bit won't be updated)
2. try to age the memory by /sys/kernel/debug/lru_gen

Run above steps with LRU_GEN_NONLEAF_YOUNG(0x4) and not respectively
(switching by /sys/kernel/mm/lru_gen/enabled). LRU_GEN_NONLEAF_YOUNG
will clear and test the PMD AF bit on page walking for aging,
otherwise will clear and test the PTE AF bit for aging. In this case
LRU_GEN_NONLEAF_YOUNG will improve the efficiency of page scanning
since pages won't be accessed and we don't need to scan each PTE.
Observed ~40% time saved for 1GiB memory on our emulated platform
with LRU_GEN_NONLEAF_YOUNG.

For lru-gen aging:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/mm/multigen_lru.rst?h=v6.11-rc1#n94

Change since v3:
Address the comments per Catalin. Add tags for Patch 1/5 and 2/5.
- Make HAFT a ARM64_CPUCAP_SYSTEM_FEATURE feature then:
  o checking the feature will be more efficient
  o avoid race between onlining a non-HAFT CPU when using the HAFT features
- Set table AF for task entries as well
- Set TCR2.HAFT unconditionally
Link: https://lore.kernel.org/linux-arm-kernel/20241022092734.59984-1-yangyicong@huawei.com/

Change since v2:
- Address comments per Will and Catalin:
  o detect and enable the feature in __cpu_setup()
  o allow online the CPU that doesn't have this feature and mismatch with the boot CPU
  o only advertise the feature if it's enabled system widely
  o set AF bit for kernel page table entries to save later hardware update
  o warn unexpected pmdp_test_and_clear_young()
- Update all the new AA64MMFR1_EL1 fields per Mark
Link: https://lore.kernel.org/linux-arm-kernel/20240814092333.7727-1-yangyicong@huawei.com/

Change since v1:
- Address comments from Marc, improve comments/Kconfig, clean code. Thanks for
  the comments.
Link: https://lore.kernel.org/linux-arm-kernel/20240802093458.32683-1-yangyicong@huawei.com/

Yicong Yang (5):
  arm64/sysreg: Update ID_AA64MMFR1_EL1 register
  arm64: setup: name 'tcr2' register
  arm64: Add support for FEAT_HAFT
  arm64: Enable ARCH_HAS_NONLEAF_PMD_YOUNG
  arm64: pgtable: Warn unexpected pmdp_test_and_clear_young()

 arch/arm64/Kconfig                     | 16 ++++++++++++++++
 arch/arm64/include/asm/cpufeature.h    |  6 ++++++
 arch/arm64/include/asm/pgalloc.h       | 12 +++++++-----
 arch/arm64/include/asm/pgtable-hwdef.h |  4 ++++
 arch/arm64/include/asm/pgtable.h       | 10 ++++++++--
 arch/arm64/kernel/cpufeature.c         | 15 +++++++++++++++
 arch/arm64/mm/fixmap.c                 |  9 ++++++---
 arch/arm64/mm/mmu.c                    |  8 ++++----
 arch/arm64/mm/proc.S                   | 16 ++++++++++++++--
 arch/arm64/tools/cpucaps               |  1 +
 arch/arm64/tools/sysreg                |  4 ++++
 11 files changed, 85 insertions(+), 16 deletions(-)