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

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Message-ID: <e93fde18-b5e5-474c-9f5e-1c9a340775ba@linux.ibm.com>
Date: Fri, 6 Feb 2026 16:12:30 +0100
From: Janosch Frank <frankja@...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, 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 2/6/26 15:35, 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>

Acked-by: Janosch Frank <frankja@...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);
>