[PATCH v2 0/2] Support Armv8.9/v9.4 FEAT_HAFT

[Yicong Yang]

From: Yicong Yang <yangyicong at 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 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 (2):
  arm64: Add support for FEAT_HAFT
  arm64: Enable ARCH_HAS_NONLEAF_PMD_YOUNG

 arch/arm64/Kconfig               | 20 ++++++++++++++++++++
 arch/arm64/include/asm/pgtable.h | 14 ++++++++++++--
 arch/arm64/kernel/cpufeature.c   | 26 ++++++++++++++++++++++++++
 arch/arm64/tools/cpucaps         |  1 +
 arch/arm64/tools/sysreg          |  1 +
 5 files changed, 60 insertions(+), 2 deletions(-)

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2.24.0