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Peter Anvin" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org Subject: [PATCH v2 5/5] mm: Do not map the shadow stack as THP Date: Wed, 25 Feb 2026 16:14:02 +0000 Message-ID: <20260225161404.3157851-6-catalin.marinas@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260225161404.3157851-1-catalin.marinas@arm.com> References: <20260225161404.3157851-1-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 1B7FA140014 X-Stat-Signature: o3gxhc8r4396q7tbkoxwusaaiojrae44 X-HE-Tag: 1772036069-875084 X-HE-Meta: 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 exL0kdw8 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Tested-by: Deepak Gupta Reviewed-by: Mark Brown Acked-by: David Hildenbrand (Arm) Cc: Andrew Morton --- mm/util.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/mm/util.c b/mm/util.c index 51f7f417e91f..419cb81ab353 100644 --- a/mm/util.c +++ b/mm/util.c @@ -629,14 +629,18 @@ unsigned long vm_mmap_shadow_stack(unsigned long addr, unsigned long len, { struct mm_struct *mm = current->mm; unsigned long ret, unused; + vm_flags_t vm_flags = VM_SHADOW_STACK; flags |= MAP_ANONYMOUS | MAP_PRIVATE; if (addr) flags |= MAP_FIXED_NOREPLACE; + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) + vm_flags |= VM_NOHUGEPAGE; + mmap_write_lock(mm); ret = do_mmap(NULL, addr, len, PROT_READ | PROT_WRITE, flags, - VM_SHADOW_STACK, 0, &unused, NULL); + vm_flags, 0, &unused, NULL); mmap_write_unlock(mm); return ret;