KVM: s390: vsie: fix race during shadow creation

[ Upstream commit fe752331d4b361d43cfd0b89534b4b2176057c32 ]

Right now it is possible to see gmap->private being zero in
kvm_s390_vsie_gmap_notifier resulting in a crash.  This is due to the
fact that we add gmap->private == kvm after creation:

static int acquire_gmap_shadow(struct kvm_vcpu *vcpu,
                               struct vsie_page *vsie_page)
{
[...]
        gmap = gmap_shadow(vcpu->arch.gmap, asce, edat);
        if (IS_ERR(gmap))
                return PTR_ERR(gmap);
        gmap->private = vcpu->kvm;

Let children inherit the private field of the parent.

Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization")
Cc: <stable@vger.kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20231220125317.4258-1-borntraeger@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index b2dbf08a961e5ab14c1cf9c0a0578d571b216e78..d90c818a9ae712e2378822e0e9fb0dc9eff6f770 100644 (file)
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1216,7 +1216,6 @@ static int acquire_gmap_shadow(struct kvm_vcpu *vcpu,
        gmap = gmap_shadow(vcpu->arch.gmap, asce, edat);
        if (IS_ERR(gmap))
                return PTR_ERR(gmap);
-       gmap->private = vcpu->kvm;
        vcpu->kvm->stat.gmap_shadow_create++;
        WRITE_ONCE(vsie_page->gmap, gmap);
        return 0;

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 243f673fa65151b5c33217391b1b6b99f800c665..662cf23a1b44b253c74455bacf3f50e4d0b1fd98 100644 (file)
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -1675,6 +1675,7 @@ struct gmap *gmap_shadow(struct gmap *parent, unsigned long asce,
                return ERR_PTR(-ENOMEM);
        new->mm = parent->mm;
        new->parent = gmap_get(parent);
+       new->private = parent->private;
        new->orig_asce = asce;
        new->edat_level = edat_level;
        new->initialized = false;