Re: [PATCH 5/5] mm: Do not map the shadow stack as THP
From: "David Hildenbrand (Arm)" <david@kernel.org>
Date: 2026-02-25 13:34:54
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On 2/24/26 18:57, Catalin Marinas wrote:
The default shadow stack size allocated on first prctl() for the main
thread or subsequently on clone() is either half of RLIMIT_STACK or half
of a thread's stack size (for arm64). Both of these are likely to be
suitable for a THP allocation and the kernel is more aggressive in
creating such mappings. However, it does not make much sense to use a
huge page. It didn't make sense for the normal stacks either, see commit
c4608d1bf7c6 ("mm: mmap: map MAP_STACK to VM_NOHUGEPAGE").
Force VM_NOHUGEPAGE when allocating/mapping the shadow stack. As per
commit 7190b3c8bd2b ("mm: mmap: map MAP_STACK to VM_NOHUGEPAGE only if
THP is enabled"), only pass this flag if TRANSPARENT_HUGEPAGE is enabled
as not to confuse CRIU tools.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
---Acked-by: David Hildenbrand (Arm) <david@kernel.org> -- Cheers, David