linux-kernel - Re: [PATCH v2] liveupdate: separate memfd support into LIVEUPDATE

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Message-ID: <CA+CK2bB_7vdtWt9cccV2icV2gdyM5UaD=BnAOhWnKx9WFKWSUQ@mail.gmail.com>
Date: Tue, 30 Dec 2025 11:07:41 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, pratyush@...nel.org
Subject: Re: [PATCH v2] liveupdate: separate memfd support into LIVEUPDATE_MEMFD

On Tue, Dec 30, 2025 at 10:30 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> On Tue, Dec 30, 2025 at 09:53:21AM -0500, Pasha Tatashin wrote:
> > Decouple memfd preservation support from the core Live Update
> > Orchestrator configuration.
> >
> > Previously, enabling CONFIG_LIVEUPDATE forced a dependency on
> > CONFIG_SHMEM and unconditionally compiled memfd_luo.o. However, Live
> > Update may be used for purposes that do not require memfd-backed memory
> > preservation.
> >
> > Introduce CONFIG_LIVEUPDATE_MEMFD to gate memfd_luo.o. This moves the
> > SHMEM and MEMFD_CREATE dependencies to the specific feature that needs
> > them, allowing the base LIVEUPDATE option to be selected independently
> > of shared memory support.
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> > Reviewed-by: Pratyush Yadav <pratyush@...nel.org>
> > ---
> > Changes v2:
> > - Updated testing config
> > - Added review-by
> >
> >  kernel/liveupdate/Kconfig                 | 16 +++++++++++++++-
> >  mm/Makefile                               |  2 +-
> >  tools/testing/selftests/liveupdate/config |  1 +
> >  3 files changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig
> > index d2aeaf13c3ac..9a1a8cdcf16c 100644
> > --- a/kernel/liveupdate/Kconfig
> > +++ b/kernel/liveupdate/Kconfig
> > @@ -54,7 +54,6 @@ config KEXEC_HANDOVER_ENABLE_DEFAULT
> >  config LIVEUPDATE
> >       bool "Live Update Orchestrator"
> >       depends on KEXEC_HANDOVER
> > -     depends on SHMEM
> >       help
> >         Enable the Live Update Orchestrator. Live Update is a mechanism,
> >         typically based on kexec, that allows the kernel to be updated
> > @@ -73,4 +72,19 @@ config LIVEUPDATE
> >
> >         If unsure, say N.
> >
> > +config LIVEUPDATE_MEMFD
> > +     bool "Live update support for memfd"
> > +     depends on LIVEUPDATE
> > +     depends on MEMFD_CREATE
> > +     depends on SHMEM
>
> Maybe also
>
>         default LIVEUPDATE

Yeah, I like this idea, let me make the change, and send v3.

Pasha