Re: [PATCH v5 32/38] mm/madvise: use predicates for madvise(..., MADV_DOFORK)
flat view
From: "David Hildenbrand (Arm)" <david@kernel.org>
Date: 2026-10-12 18:49:19
Also in:
bpf, dri-devel, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-riscv, linux-s390, linux-scsi, linux-sound, linux-trace-kernel, linux-usb, linuxppc-dev, lkml, selinux, sparclinux
On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote:
Make it clear what we're blocking in MADV_DOFORK. Previously we simply
disallowed VM_SPECIAL i.e. mappings not managed by core mm, fixed mappings
and
VMA_IO_BIT.
Now the invariant is established that mm-managed mappings may not set
VMA_IO_BIT, the VMA_IO_BIT check is redundant.
The rest is equivalent to testing for a fixed or non-mm-managed mapping,
i.e. exactly the same check as whether the VMA is permitted to be merged.
This was established by commit 0b2758f48f22 ("Require (reasonably) normal
mappings for MADV_DOFORK") containing my hands-down favourite call out of
all time.
Express the same thing differently - if we wouldn't be allowed to merge it,
then we aren't allowed to manipulate CoW behaviour on fork.
No functional change intended.
Acked-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>Acked-by: David Hildenbrand (Arm) <david@kernel.org> -- Cheers, David