Re: [PATCH v15 01/11] mm/Kconfig: changes for migrate on fault for device pages

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] mm: DEVICE_MIGRATION selects HMM_MIRROR without depends on MMU constraint
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commit d98d7483ad3c2031ffcf056a41d08580cd84769d
Author: Mika Penttilä <mpenttil@redhat.com>

mm/Kconfig: changes for migrate on fault for device pages

This commit modifies the memory management Kconfig to have DEVICE_MIGRATION
explicitly select HMM_MIRROR. This ensures HMM is enabled for the unified
HMM and migrate_device page table walks.

> diff --git a/mm/Kconfig b/mm/Kconfig
> index 604c58199acbf..b7a485beb9a78 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -687,6 +687,7 @@ config MIGRATION
>  
>  config DEVICE_MIGRATION
>  	def_bool MIGRATION && ZONE_DEVICE
> +	select HMM_MIRROR

[Severity: Low]
Does selecting HMM_MIRROR under DEVICE_MIGRATION require an explicit
dependency on MMU?

When a Kconfig symbol uses select, it is expected to have dependencies
compatible with the selected symbol's dependencies. HMM_MIRROR explicitly
depends on MMU, but DEVICE_MIGRATION lacks an explicit depends on MMU or
depends on MIGRATION constraint.

While DEVICE_MIGRATION is currently only enabled via its default expression
which transitively requires MMU, a default value expression does not act as
a dependency constraint against a select operation. If a future patch were
to forcefully select DEVICE_MIGRATION on a non-MMU architecture, it would
bypass the def_bool and enable HMM_MIRROR without its required MMU
dependency.

Could this structural risk be avoided by adding an explicit depends on MMU
to DEVICE_MIGRATION?

>  config ARCH_ENABLE_HUGEPAGE_MIGRATION
>  	bool

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Sashiko AI review · https://sashiko.dev/#/patchset/20260924065313.899730-1-mpenttil@redhat.com?part=1