[PATCH 5.5 145/257] KVM: s390: vsie: Fix delivery of addressing exceptions

[Greg Kroah-Hartman]

From: David Hildenbrand <david@xxxxxxxxxx>

commit 4d4cee96fb7a3cc53702a9be8299bf525be4ee98 upstream.

Whenever we get an -EFAULT, we failed to read in guest 2 physical
address space. Such addressing exceptions are reported via a program
intercept to the nested hypervisor.

We faked the intercept, we have to return to guest 2. Instead, right
now we would be returning -EFAULT from the intercept handler, eventually
crashing the VM.
the correct thing to do is to return 1 as rc == 1 is the internal
representation of "we have to go back into g2".

Addressing exceptions can only happen if the g2->g3 page tables
reference invalid g2 addresses (say, either a table or the final page is
not accessible - so something that basically never happens in sane
environments.

Identified by manual code inspection.

Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.8+
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200403153050.20569-3-david@xxxxxxxxxx
Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
[borntraeger@xxxxxxxxxx: fix patch description]
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/s390/kvm/vsie.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcp
 		scb_s->iprcc = PGM_ADDRESSING;
 		scb_s->pgmilc = 4;
 		scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4);
+		rc = 1;
 	}
 	return rc;
 }