linux-kernel - Re: [PATCH v2 4/5] KVM: s390: refactor and split some gmap helpers

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Message-ID: <5e058fd1-ccee-43c3-92eb-ad72d2dbc1f3@linux.ibm.com>
Date: Mon, 26 May 2025 13:17:35 +0200
From: Janosch Frank <frankja@...ux.ibm.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc: kvm@...r.kernel.org, linux-s390@...r.kernel.org, borntraeger@...ibm.com,
        seiden@...ux.ibm.com, nsg@...ux.ibm.com, nrb@...ux.ibm.com,
        david@...hat.com, hca@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, gor@...ux.ibm.com, schlameuss@...ux.ibm.com
Subject: Re: [PATCH v2 4/5] KVM: s390: refactor and split some gmap helpers

On 5/20/25 8:26 PM, Claudio Imbrenda wrote:
> Refactor some gmap functions; move the implementation into a separate
> file with only helper functions. The new helper functions work on vm
> addresses, leaving all gmap logic in the gmap functions, which mostly
> become just wrappers.
> 
> The whole gmap handling is going to be moved inside KVM soon, but the
> helper functions need to touch core mm functions, and thus need to
> stay in the core of kernel.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>   MAINTAINERS                          |   2 +
>   arch/s390/include/asm/gmap_helpers.h |  18 ++
>   arch/s390/kvm/diag.c                 |  11 +-
>   arch/s390/kvm/kvm-s390.c             |   5 +-
>   arch/s390/mm/Makefile                |   2 +
>   arch/s390/mm/gmap.c                  |  46 ++---
>   arch/s390/mm/gmap_helpers.c          | 259 +++++++++++++++++++++++++++
>   7 files changed, 302 insertions(+), 41 deletions(-)
>   create mode 100644 arch/s390/include/asm/gmap_helpers.h
>   create mode 100644 arch/s390/mm/gmap_helpers.c

[...]

> diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
> index 9726b91fe7e4..bd0401cc7ca5 100644
> --- a/arch/s390/mm/Makefile
> +++ b/arch/s390/mm/Makefile
> @@ -12,3 +12,5 @@ obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
>   obj-$(CONFIG_PTDUMP)		+= dump_pagetables.o
>   obj-$(CONFIG_PGSTE)		+= gmap.o
>   obj-$(CONFIG_PFAULT)		+= pfault.o
> +
> +obj-$(subst m,y,$(CONFIG_KVM))	+= gmap_helpers.o

So gmap.o depends on PGSTE but gmap_helpers.o depends on KVM.
Yes, PGSTE is Y if KVM is set, but this looks really strange.


@Heiko:
Can we move away from CONFIG_PGSTE and start using CONFIG_KVM instead?
Well, maybe this goes away with Claudio's rework anyway.