KVM: s390: Remove false WARN_ON_ONCE for the PQAP instruction

commit 5615e74f48dcc982655543e979b6c3f3f877e6f6 upstream.

In LPAR we will only get an intercept for FC==3 for the PQAP
instruction. Running nested under z/VM can result in other intercepts as
well as ECA_APIE is an effective bit: If one hypervisor layer has
turned this bit off, the end result will be that we will get intercepts for
all function codes. Usually the first one will be a query like PQAP(QCI).
So the WARN_ON_ONCE is not right. Let us simply remove it.

Cc: Pierre Morel <pmorel@linux.ibm.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>
Cc: stable@vger.kernel.org # v5.3+
Fixes: e5282de93105 ("s390: ap: kvm: add PQAP interception for AQIC")
Link: https://lore.kernel.org/kvm/20200505083515.2720-1-borntraeger@de.ibm.com
Reported-by: Qian Cai <cailca@icloud.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index ed52ffa..560310e 100644 (file)
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -626,10 +626,12 @@ static int handle_pqap(struct kvm_vcpu *vcpu)
         * available for the guest are AQIC and TAPQ with the t bit set
         * since we do not set IC.3 (FIII) we currently will only intercept
         * the AQIC function code.
+        * Note: running nested under z/VM can result in intercepts for other
+        * function codes, e.g. PQAP(QCI). We do not support this and bail out.
         */
        reg0 = vcpu->run->s.regs.gprs[0];
        fc = (reg0 >> 24) & 0xff;
-       if (WARN_ON_ONCE(fc != 0x03))
+       if (fc != 0x03)
                return -EOPNOTSUPP;
 
        /* PQAP instruction is allowed for guest kernel only */