KVM: s390: ucontrol: export page faults to user

This patch introduces a new exit reason in the kvm_run structure
named KVM_EXIT_S390_UCONTROL. This exit indicates, that a virtual cpu
has regognized a fault on the host page table. The idea is that
userspace can handle this fault by mapping memory at the fault
location into the cpu's address space and then continue to run the
virtual cpu.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 28 insertions, 5 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 2d3248895def..af05328aca25 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -493,8 +493,10 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
         return -EINVAL; /* not implemented yet */
 }
 
-static void __vcpu_run(struct kvm_vcpu *vcpu)
+static int __vcpu_run(struct kvm_vcpu *vcpu)
 {
+        int rc;
+
         memcpy(&vcpu->arch.sie_block->gg14, &vcpu->arch.guest_gprs[14], 16);
 
         if (need_resched())
@@ -511,9 +513,15 @@ static void __vcpu_run(struct kvm_vcpu *vcpu)
         local_irq_enable();
         VCPU_EVENT(vcpu, 6, "entering sie flags %x",
                    atomic_read(&vcpu->arch.sie_block->cpuflags));
-        if (sie64a(vcpu->arch.sie_block, vcpu->arch.guest_gprs)) {
-                VCPU_EVENT(vcpu, 3, "%s", "fault in sie instruction");
-                kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
+        rc = sie64a(vcpu->arch.sie_block, vcpu->arch.guest_gprs);
+        if (rc) {
+                if (kvm_is_ucontrol(vcpu->kvm)) {
+                        rc = SIE_INTERCEPT_UCONTROL;
+                } else {
+                        VCPU_EVENT(vcpu, 3, "%s", "fault in sie instruction");
+                        kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
+                        rc = 0;
+                }
         }
         VCPU_EVENT(vcpu, 6, "exit sie icptcode %d",
                    vcpu->arch.sie_block->icptcode);
@@ -522,6 +530,7 @@ static void __vcpu_run(struct kvm_vcpu *vcpu)
         local_irq_enable();
 
         memcpy(&vcpu->arch.guest_gprs[14], &vcpu->arch.sie_block->gg14, 16);
+        return rc;
 }
 
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
@@ -542,6 +551,7 @@ rerun_vcpu:
         case KVM_EXIT_UNKNOWN:
         case KVM_EXIT_INTR:
         case KVM_EXIT_S390_RESET:
+        case KVM_EXIT_S390_UCONTROL:
                 break;
         default:
                 BUG();
@@ -553,7 +563,9 @@ rerun_vcpu:
         might_fault();
 
         do {
-                __vcpu_run(vcpu);
+                rc = __vcpu_run(vcpu);
+                if (rc)
+                        break;
                 rc = kvm_handle_sie_intercept(vcpu);
         } while (!signal_pending(current) && !rc);
 
@@ -565,6 +577,16 @@ rerun_vcpu:
                 rc = -EINTR;
         }
 
+#ifdef CONFIG_KVM_S390_UCONTROL
+        if (rc == SIE_INTERCEPT_UCONTROL) {
+                kvm_run->exit_reason = KVM_EXIT_S390_UCONTROL;
+                kvm_run->s390_ucontrol.trans_exc_code =
+                        current->thread.gmap_addr;
+                kvm_run->s390_ucontrol.pgm_code = 0x10;
+                rc = 0;
+        }
+#endif
+
         if (rc == -EOPNOTSUPP) {
                 /* intercept cannot be handled in-kernel, prepare kvm-run */
                 kvm_run->exit_reason         = KVM_EXIT_S390_SIEIC;
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 45b236a7c730..62aa5f19bb98 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -26,6 +26,7 @@ typedef int (*intercept_handler_t)(struct kvm_vcpu *vcpu);
 
 /* negativ values are error codes, positive values for internal conditions */
 #define SIE_INTERCEPT_RERUNVCPU         (1<<0)
+#define SIE_INTERCEPT_UCONTROL          (1<<1)
 int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu);
 
 #define VM_EVENT(d_kvm, d_loglevel, d_string, d_args...)\