KVM: s390: allow user space to handle instr 0x0000

We will use illegal instruction 0x0000 for handling 2 byte sw breakpoints
from user space. As it can be enabled dynamically via a capability,
let's move setting of ICTL_OPEREXC to the post creation step, so we avoid
any races when enabling that capability just while adding new cpus.

Acked-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

5 files changed, 43 insertions, 2 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index c4d2fb0e28de..299306db5d84 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3857,6 +3857,19 @@ as a broadcast even in x2APIC mode in order to support physical x2APIC
 without interrupt remapping.  This is undesirable in logical mode,
 where 0xff represents CPUs 0-7 in cluster 0.
 
+7.8 KVM_CAP_S390_USER_INSTR0
+
+Architectures: s390
+Parameters: none
+
+With this capability enabled, all illegal instructions 0x0000 (2 bytes) will
+be intercepted and forwarded to user space. User space can use this
+mechanism e.g. to realize 2-byte software breakpoints. The kernel will
+not inject an operating exception for these instructions, user space has
+to take care of that.
+
+This capability can be enabled dynamically even if VCPUs were already
+created and are running.
 
 8. Other capabilities.
 ----------------------
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 946fc86202fd..183b01727de4 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -43,6 +43,7 @@
 /* s390-specific vcpu->requests bit members */
 #define KVM_REQ_ENABLE_IBS         8
 #define KVM_REQ_DISABLE_IBS        9
+#define KVM_REQ_ICPT_OPEREXC       10
 
 #define SIGP_CTRL_C             0x80
 #define SIGP_CTRL_SCN_MASK      0x3f
@@ -666,6 +667,7 @@ struct kvm_arch{
         int user_cpu_state_ctrl;
         int user_sigp;
         int user_stsi;
+        int user_instr0;
         struct s390_io_adapter *adapters[MAX_S390_IO_ADAPTERS];
         wait_queue_head_t ipte_wq;
         int ipte_lock_count;
diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 850be47c4cc9..7a2f1551bc39 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -359,6 +359,9 @@ static int handle_operexc(struct kvm_vcpu *vcpu)
             test_kvm_facility(vcpu->kvm, 74))
                 return handle_sthyi(vcpu);
 
+        if (vcpu->arch.sie_block->ipa == 0 && vcpu->kvm->arch.user_instr0)
+                return -EOPNOTSUPP;
+
         return kvm_s390_inject_program_int(vcpu, PGM_OPERATION);
 }
 
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index d42428c11794..63ac7c1641a7 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -364,6 +364,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
         case KVM_CAP_S390_USER_STSI:
         case KVM_CAP_S390_SKEYS:
         case KVM_CAP_S390_IRQ_STATE:
+        case KVM_CAP_S390_USER_INSTR0:
                 r = 1;
                 break;
         case KVM_CAP_S390_MEM_OP:
@@ -456,6 +457,16 @@ out:
         return r;
 }
 
+static void icpt_operexc_on_all_vcpus(struct kvm *kvm)
+{
+        unsigned int i;
+        struct kvm_vcpu *vcpu;
+
+        kvm_for_each_vcpu(i, vcpu, kvm) {
+                kvm_s390_sync_request(KVM_REQ_ICPT_OPEREXC, vcpu);
+        }
+}
+
 static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 {
         int r;
@@ -507,6 +518,12 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
                 kvm->arch.user_stsi = 1;
                 r = 0;
                 break;
+        case KVM_CAP_S390_USER_INSTR0:
+                VM_EVENT(kvm, 3, "%s", "ENABLE: CAP_S390_USER_INSTR0");
+                kvm->arch.user_instr0 = 1;
+                icpt_operexc_on_all_vcpus(kvm);
+                r = 0;
+                break;
         default:
                 r = -EINVAL;
                 break;
@@ -1836,6 +1853,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
                 vcpu->arch.gmap = vcpu->kvm->arch.gmap;
                 sca_add_vcpu(vcpu);
         }
+        if (test_kvm_facility(vcpu->kvm, 74) || vcpu->kvm->arch.user_instr0)
+                vcpu->arch.sie_block->ictl |= ICTL_OPEREXC;
         /* make vcpu_load load the right gmap on the first trigger */
         vcpu->arch.enabled_gmap = vcpu->arch.gmap;
 }
@@ -1923,8 +1942,6 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
         }
         vcpu->arch.sie_block->riccbd = (unsigned long) &vcpu->run->s.regs.riccb;
         vcpu->arch.sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
-        if (test_kvm_facility(vcpu->kvm, 74))
-                vcpu->arch.sie_block->ictl |= ICTL_OPEREXC;
 
         if (vcpu->kvm->arch.use_cmma) {
                 rc = kvm_s390_vcpu_setup_cmma(vcpu);
@@ -2369,6 +2386,11 @@ retry:
                 goto retry;
         }
 
+        if (kvm_check_request(KVM_REQ_ICPT_OPEREXC, vcpu)) {
+                vcpu->arch.sie_block->ictl |= ICTL_OPEREXC;
+                goto retry;
+        }
+
         /* nothing to do, just clear the request */
         clear_bit(KVM_REQ_UNHALT, &vcpu->requests);
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 4f8030e5b05d..70941f4ab6d8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -867,6 +867,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_VCPU_ATTRIBUTES 127
 #define KVM_CAP_MAX_VCPU_ID 128
 #define KVM_CAP_X2APIC_API 129
+#define KVM_CAP_S390_USER_INSTR0 130
 
 #ifdef KVM_CAP_IRQ_ROUTING