Re: [PATCH 14/39] mm/vma: add vma[_flags]_is_kernel_owned() predicates

Rather than referring to VMA flags with uncertain meaning, add a new
predicate that explicitly describes what possession of the VMA_PFNMAP_BIT
or VMA_MIXEDMAP_BIT flags mean, and then refer to that function for
determining VMA mergeability.

Either flag means the contents of the mapping are owned by the kernel,
usually a driver, rather than by the core mm: the memory may be MMIO,
kernel-allocated pages or even ordinary pages the driver maps itself, but
the core must not populate, reclaim, migrate, copy-on-write or merge the
range on its own initiative.

We initially also include VMA_IO_BIT here, as by implication, these must be
kernel-owned. (mlock() also sets VMA_IO_BIT transiently on ordinary VMAs
while locking them, which is addressed later in this series.)

However the intent is to in future remove this, as no mapping should be
marked as an I/O mapping without also being marked with VMA_PFNMAP_BIT.

This forms the basis of further work intended to improve how we express VMA
properties such as this.

Also update the VMA userland tests to reflect the change.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260908-b4-mmap-prepare-vma-flag-sanify-v1-0-dacf19cce22b@kernel.org?part=14