Re: [PATCH v1 2/3] KVM: s390: vsie: Fix race in walk_guest_tables()

["Christoph Schlameuss" <schlameuss@linux.ibm.com>]

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@linux.ibm.com>

Reviewed-by: Christoph Schlameuss <schlameuss@linux.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);
>