linux-kernel - Re: [PATCH v3 18/23] KVM: s390: Switch to new gmap

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Message-ID: <20251118151818.9674C62-hca@linux.ibm.com>
Date: Tue, 18 Nov 2025 16:18:18 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, nsg@...ux.ibm.com, nrb@...ux.ibm.com,
        seiden@...ux.ibm.com, schlameuss@...ux.ibm.com, svens@...ux.ibm.com,
        agordeev@...ux.ibm.com, gor@...ux.ibm.com, david@...hat.com,
        gerald.schaefer@...ux.ibm.com
Subject: Re: [PATCH v3 18/23] KVM: s390: Switch to new gmap

On Thu, Nov 06, 2025 at 05:11:12PM +0100, Claudio Imbrenda wrote:
> Switch KVM/s390 to use the new gmap code.
> 
> Remove includes to <gmap.h> and include "gmap.h" instead; fix all the
> existing users of the old gmap functions to use the new ones instead.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>  arch/s390/Kconfig                   |   2 +-
>  arch/s390/include/asm/kvm_host.h    |   5 +-
>  arch/s390/include/asm/mmu_context.h |   4 -
>  arch/s390/include/asm/tlb.h         |   3 -
>  arch/s390/kvm/Makefile              |   2 +-
>  arch/s390/kvm/diag.c                |   2 +-
>  arch/s390/kvm/gaccess.c             | 552 +++++++++++----------
>  arch/s390/kvm/gaccess.h             |  16 +-
>  arch/s390/kvm/gmap-vsie.c           | 141 ------
>  arch/s390/kvm/gmap.c                |   6 +-
>  arch/s390/kvm/intercept.c           |  15 +-
>  arch/s390/kvm/interrupt.c           |   2 +-
>  arch/s390/kvm/kvm-s390.c            | 727 ++++++++--------------------
>  arch/s390/kvm/kvm-s390.h            |  20 +-
>  arch/s390/kvm/priv.c                | 207 +++-----
>  arch/s390/kvm/pv.c                  |  64 +--
>  arch/s390/kvm/vsie.c                | 117 +++--
>  arch/s390/mm/gmap_helpers.c         |  29 --
>  18 files changed, 710 insertions(+), 1204 deletions(-)
>  delete mode 100644 arch/s390/kvm/gmap-vsie.c

...

> +static int _gaccess_do_shadow(struct kvm_s390_mmu_cache *mc, struct gmap *sg,
> +			      unsigned long saddr, struct pgtwalk *w)
> +{

...

> +	/*
> +	 * Skip levels that are already protected. For each level, protect
> +	 * only the page containing the entry, not the whole table.
> +	 */
> +	for (i = gl ; i > w->level; i--)
> +		gmap_protect_rmap(mc, sg, entries[i - 1].gfn, gpa_to_gfn(saddr),
> +				  entries[i - 1].pfn, i, entries[i - 1].writable);
> +

Why is it ok to ignore the potential -ENOMEM return value of
gmap_protect_rmap()?