[PATCH 29/39] mm/madvise: update is_valid_guard_vma() to use vma_can_merge()
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Date: 2026-09-08 20:16:16
Also in:
bpf, dri-devel, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fbdev, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-s390, linux-scsi, linux-sound, linux-usb, linuxppc-dev, lkml, selinux, sparclinux
Subsystem:
memory management, memory mapping - madvise (memory advice), the rest · Maintainers:
Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, David Hildenbrand, Linus Torvalds
We currently disallow the installation of lightweight guard regions in VMAs whose flags intersect VMA_SPECIAL_FLAGS or VMA_HUGETLB_BIT, or VMA_LOCKED_BIT unless allow_locked is set. hugetlb VMAs set VMA_DONTEXPAND_BIT so this was already redundant, VMA_SPECIAL_FLAGS already sufficed. However, now that VMA_IO_BIT is only set if VMA_PFNMAP or VMA_MIXEDMAP_BIT is set, this check collapses to being the equivalent of !vma_can_merge(). Update is_valid_guard_vma() to reflect this. No functional change intended. Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> --- mm/madvise.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/mm/madvise.c b/mm/madvise.c
index 2db11c832d0f..d0b14cfe38a1 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c@@ -1055,19 +1055,25 @@ static long madvise_remove(struct madvise_behavior *madv_behavior) return error; } -static bool is_valid_guard_vma(struct vm_area_struct *vma, bool allow_locked) +static bool is_valid_guard_vma(const struct vm_area_struct *vma, + bool allow_locked) { - vm_flags_t disallowed = VM_SPECIAL | VM_HUGETLB; - /* - * A user could lock after setting a guard range but that's fine, as + * A user could lock after setting a guard range but that's fine as * they'd not be able to fault in. The issue arises when we try to zap * existing locked VMAs. We don't want to do that. */ - if (!allow_locked) - disallowed |= VM_LOCKED; + if (!allow_locked && vma_test(vma, VMA_LOCKED_BIT)) + return false; + /* + * Guard regions require a VMA whose page tables are managed solely by + * the core, which is also what merging requires, so disallow any flags + * that would prevent a merge. + */ + if (!vma_can_merge(vma)) + return false; - return !(vma->vm_flags & disallowed); + return true; } static bool is_guard_pte_marker(pte_t ptent)
--
2.55.0