s390/kvm: Kick guests out of sie if prefix page host pte is touched

The guest prefix pages must be mapped writeable all the time
while SIE is running, otherwise the guest might see random
behaviour. (pinned at the pte level) Turns out that mlocking is
not enough, the page table entry (not the page) might change or
become r/o. This patch uses the gmap notifiers to kick guest
cpus out of SIE.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 2 insertions, 37 deletions

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index b7d1b2edeeb3..f0b8be0cc08d 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -174,47 +174,12 @@ static int handle_stop(struct kvm_vcpu *vcpu)
 
 static int handle_validity(struct kvm_vcpu *vcpu)
 {
-        unsigned long vmaddr;
         int viwhy = vcpu->arch.sie_block->ipb >> 16;
-        int rc;
 
         vcpu->stat.exit_validity++;
         trace_kvm_s390_intercept_validity(vcpu, viwhy);
-        if (viwhy == 0x37) {
-                vmaddr = gmap_fault(vcpu->arch.sie_block->prefix,
-                                    vcpu->arch.gmap);
-                if (IS_ERR_VALUE(vmaddr)) {
-                        rc = -EOPNOTSUPP;
-                        goto out;
-                }
-                rc = fault_in_pages_writeable((char __user *) vmaddr,
-                         PAGE_SIZE);
-                if (rc) {
-                        /* user will receive sigsegv, exit to user */
-                        rc = -EOPNOTSUPP;
-                        goto out;
-                }
-                vmaddr = gmap_fault(vcpu->arch.sie_block->prefix + PAGE_SIZE,
-                                    vcpu->arch.gmap);
-                if (IS_ERR_VALUE(vmaddr)) {
-                        rc = -EOPNOTSUPP;
-                        goto out;
-                }
-                rc = fault_in_pages_writeable((char __user *) vmaddr,
-                         PAGE_SIZE);
-                if (rc) {
-                        /* user will receive sigsegv, exit to user */
-                        rc = -EOPNOTSUPP;
-                        goto out;
-                }
-        } else
-                rc = -EOPNOTSUPP;
-
-out:
-        if (rc)
-                VCPU_EVENT(vcpu, 2, "unhandled validity intercept code %d",
-                           viwhy);
-        return rc;
+        WARN_ONCE(true, "kvm: unhandled validity intercept 0x%x\n", viwhy);
+        return -EOPNOTSUPP;
 }
 
 static int handle_instruction(struct kvm_vcpu *vcpu)