linux-kernel - Re: [PATCH v1 2/3] KVM: s390: vsie: Fix race in walk_guest

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Message-Id: <DGALW3FURCY8.DRKU9407VTTO@linux.ibm.com>
Date: Mon, 09 Feb 2026 18:27:23 +0100
From: "Christoph Schlameuss" <schlameuss@...ux.ibm.com>
To: "Claudio Imbrenda" <imbrenda@...ux.ibm.com>, <kvm@...r.kernel.org>
Cc: <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>, <gra@...ux.ibm.com>,
        <schlameuss@...ux.ibm.com>, <hca@...ux.ibm.com>, <svens@...ux.ibm.com>,
        <agordeev@...ux.ibm.com>, <gor@...ux.ibm.com>, <david@...nel.org>,
        <gerald.schaefer@...ux.ibm.com>
Subject: Re: [PATCH v1 2/3] KVM: s390: vsie: Fix race in walk_guest_tables()

On Fri Feb 6, 2026 at 3:35 PM CET, Claudio Imbrenda wrote:
> It is possible that walk_guest_tables() is called on a shadow gmap that
> has been removed already, in which case its parent will be NULL.
>
> In such case, return -EAGAIN and let the callers deal with it.
>
> Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

Reviewed-by: Christoph Schlameuss <schlameuss@...ux.ibm.com>

> ---
>  arch/s390/kvm/gaccess.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 67de47a81a87..4630b2a067ea 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -1287,7 +1287,10 @@ static int walk_guest_tables(struct gmap *sg, unsigned long saddr, struct pgtwal
>  	union asce asce;
>  	int rc;
>  
> +	if (!parent)
> +		return -EAGAIN;
>  	kvm = parent->kvm;
> +	WARN_ON(!kvm);
>  	asce = sg->guest_asce;
>  	entries = get_entries(w);
>