[PATCH v1 1/2] KVM: s390: load guest access registers in MEM_OP ioctl

[Eric Farman <farman@linux.ibm.com>]

The routine ar_translation() is called by get_vcpu_asce(), which is
called by both the instruction intercept path (where the access
registers had been loaded with the guest's values), and the MEM_OP
ioctl (which hadn't). This means that any ALET the guest expects to
be used would be ignored.

Furthermore, the logic in ar_translation() will store the contents
of the access registers back to the KVM_RUN struct. This unexpected
change of AR values can lead to problems after invoking the MEM_OP,
for example an ALET Specification Exception.

Fix this by swapping the host/guest access registers around the
MEM_OP ioctl, in the same way that the KVM_RUN ioctl does with
sync_regs()/store_regs(). The full register swap isn't needed here,
since only the access registers are used in this interface.

Suggested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index ea63ac769889..c2dfeea55dcf 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5391,6 +5391,10 @@ static long kvm_s390_vcpu_mem_op(struct kvm_vcpu *vcpu,
 			return -ENOMEM;
 	}
 
+	/* Swap host/guest access registers in the event of a MEM_OP with AR specified */
+	save_access_regs(vcpu->arch.host_acrs);
+	restore_access_regs(vcpu->run->s.regs.acrs);
+
 	acc_mode = mop->op == KVM_S390_MEMOP_LOGICAL_READ ? GACC_FETCH : GACC_STORE;
 	if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
 		r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size,
@@ -5420,6 +5424,8 @@ static long kvm_s390_vcpu_mem_op(struct kvm_vcpu *vcpu,
 		kvm_s390_inject_prog_irq(vcpu, &vcpu->arch.pgm);
 
 out_free:
+	save_access_regs(vcpu->run->s.regs.acrs);
+	restore_access_regs(vcpu->arch.host_acrs);
 	vfree(tmpbuf);
 	return r;
 }
-- 
2.40.1