Re: [PATCH 30/39] mm/vma: introduce vma[_flags]_is_persistent()

[sashiko-bot@kernel.org]

> Introduce vma[_flags]_is_persistent() for the purposes of identifying
> mappings that are persistent in the sense that bytes to the mapping stay
> there, and bytes read from the mapping are the same unless changed by
> actions taken by userland.
> 
> Kernel-owned mappings do not fall into this category, as their owner may
> change the contents without the user having initiated it, and nor of course
> does memory-mapped I/O.
> 
> We exclude fixed mappings as these are singled out as being unmergeable and
> so cannot be guaranteed to persist user data.
> 
> hugetlb mappings are fixed mappings, but their contents are entirely the
> user's, so they are explicitly carved out as persistent, as the MADV_DODUMP
> check already does.
> 
> It excludes droppable mappings, which by their nature are ephemeral.
> 
> Use this functionality to update the madvise MADV_DODUMP check to test for
> persistence rather than open-coding this.
> 
> This replaces the VM_SPECIAL check which means it no longer checks for
> VMA_IO_BIT, however this is safe as we have established the invariant that
> only kernel-owned mappings may set VMA_IO_BIT, so we implicitly include
> these.
> 
> 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=30