[PATCH 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables

[Muhammad Usama Anjum]

Stacks and page tables are always accessed with the match‑all tag,
so assigning a new random tag every time at allocation and setting
invalid tag at deallocation time, just adds overhead without improving
the detection.

With __GFP_SKIP_KASAN the page keeps its poison tag and KASAN_TAG_KERNEL
(match-all tag) is stored in the page flags while keeping the poison tag
in the hardware. The benefit of it is that 256 tag setting instruction
per 4 kB page aren't needed at allocation and deallocation time.

Thus match‑all pointers still work, while non‑match tags (other than
poison tag) still fault.

__GFP_SKIP_KASAN only skips for KASAN_HW_TAGS mode, so coverage is
unchanged.

Benchmark:
The benchmark has two modes. In thread mode, the child process forks
and creates N threads. In pgtable mode, the parent maps and faults a
specified memory size and then forks repeatedly with children exiting
immediately.

Thread benchmark:
2000 iterations, 2000 threads:	2.575 s → 2.229 s (~13.4% faster)

The pgtable samples:
- 2048 MB, 2000 iters		19.08 s → 17.62 s (~7.6% faster)

Muhammad Usama Anjum (3):
  vmalloc: add __GFP_SKIP_KASAN support
  fork: skip MTE tagging for kernel stacks
  mm: SKIP KASAN for page table allocations

 include/asm-generic/pgalloc.h | 2 +-
 kernel/fork.c                 | 8 +++++---
 mm/vmalloc.c                  | 8 ++++++--
 3 files changed, 12 insertions(+), 6 deletions(-)

-- 
2.47.3