KVM: s390: forward most SIGP orders to user space

Most SIGP orders are handled partially in kernel and partially in
user space. In order to:
- Get a correct SIGP SET PREFIX handler that informs user space
- Avoid race conditions between concurrently executed SIGP orders
- Serialize SIGP orders per VCPU

We need to handle all "slow" SIGP orders in user space. The remaining
ones to be handled completely in kernel are:
- SENSE
- SENSE RUNNING
- EXTERNAL CALL
- EMERGENCY SIGNAL
- CONDITIONAL EMERGENCY SIGNAL
According to the PoP, they have to be fast. They can be executed
without conflicting to the actions of other pending/concurrently
executing orders (e.g. STOP vs. START).

This patch introduces a new capability that will - when enabled -
forward all but the mentioned SIGP orders to user space. The
instruction counters in the kernel are still updated.

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, 76 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 3ca6e0e9a769..df19837e94d4 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3225,3 +3225,23 @@ userspace from doing that.
 If the hcall number specified is not one that has an in-kernel
 implementation, the KVM_ENABLE_CAP ioctl will fail with an EINVAL
 error.
+
+7.2 KVM_CAP_S390_USER_SIGP
+
+Architectures: s390
+Parameters: none
+
+This capability controls which SIGP orders will be handled completely in user
+space. With this capability enabled, all fast orders will be handled completely
+in the kernel:
+- SENSE
+- SENSE RUNNING
+- EXTERNAL CALL
+- EMERGENCY SIGNAL
+- CONDITIONAL EMERGENCY SIGNAL
+
+All other orders will be handled completely in user space.
+
+Only privileged operation exceptions will be checked for in the kernel (or even
+in the hardware prior to interception). If this capability is not enabled, the
+old way of handling SIGP orders is used (partially in kernel and user space).
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index b6170520380b..a2dcd0e099f7 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -521,6 +521,7 @@ struct kvm_arch{
         int use_irqchip;
         int use_cmma;
         int user_cpu_state_ctrl;
+        int user_sigp;
         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/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index bfb2b990da9b..3677b8ca647f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -166,6 +166,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
         case KVM_CAP_S390_IRQCHIP:
         case KVM_CAP_VM_ATTRIBUTES:
         case KVM_CAP_MP_STATE:
+        case KVM_CAP_S390_USER_SIGP:
                 r = 1;
                 break;
         case KVM_CAP_NR_VCPUS:
@@ -254,6 +255,10 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
                 kvm->arch.use_irqchip = 1;
                 r = 0;
                 break;
+        case KVM_CAP_S390_USER_SIGP:
+                kvm->arch.user_sigp = 1;
+                r = 0;
+                break;
         default:
                 r = -EINVAL;
                 break;
diff --git a/arch/s390/kvm/sigp.c b/arch/s390/kvm/sigp.c
index 1524be9120ad..23b1e86b2122 100644
--- a/arch/s390/kvm/sigp.c
+++ b/arch/s390/kvm/sigp.c
@@ -371,6 +371,53 @@ static int handle_sigp_dst(struct kvm_vcpu *vcpu, u8 order_code,
         return rc;
 }
 
+static int handle_sigp_order_in_user_space(struct kvm_vcpu *vcpu, u8 order_code)
+{
+        if (!vcpu->kvm->arch.user_sigp)
+                return 0;
+
+        switch (order_code) {
+        case SIGP_SENSE:
+        case SIGP_EXTERNAL_CALL:
+        case SIGP_EMERGENCY_SIGNAL:
+        case SIGP_COND_EMERGENCY_SIGNAL:
+        case SIGP_SENSE_RUNNING:
+                return 0;
+        /* update counters as we're directly dropping to user space */
+        case SIGP_STOP:
+                vcpu->stat.instruction_sigp_stop++;
+                break;
+        case SIGP_STOP_AND_STORE_STATUS:
+                vcpu->stat.instruction_sigp_stop_store_status++;
+                break;
+        case SIGP_STORE_STATUS_AT_ADDRESS:
+                vcpu->stat.instruction_sigp_store_status++;
+                break;
+        case SIGP_SET_PREFIX:
+                vcpu->stat.instruction_sigp_prefix++;
+                break;
+        case SIGP_START:
+                vcpu->stat.instruction_sigp_start++;
+                break;
+        case SIGP_RESTART:
+                vcpu->stat.instruction_sigp_restart++;
+                break;
+        case SIGP_INITIAL_CPU_RESET:
+                vcpu->stat.instruction_sigp_init_cpu_reset++;
+                break;
+        case SIGP_CPU_RESET:
+                vcpu->stat.instruction_sigp_cpu_reset++;
+                break;
+        default:
+                vcpu->stat.instruction_sigp_unknown++;
+        }
+
+        VCPU_EVENT(vcpu, 4, "sigp order %u: completely handled in user space",
+                   order_code);
+
+        return 1;
+}
+
 int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu)
 {
         int r1 = (vcpu->arch.sie_block->ipa & 0x00f0) >> 4;
@@ -385,6 +432,8 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu)
                 return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
 
         order_code = kvm_s390_get_base_disp_rs(vcpu);
+        if (handle_sigp_order_in_user_space(vcpu, order_code))
+                return -EOPNOTSUPP;
 
         if (r1 % 2)
                 parameter = vcpu->run->s.regs.gprs[r1];
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index adc24a3fd23e..37f71c3040c3 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -759,6 +759,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_PPC_FIXUP_HCALL 103
 #define KVM_CAP_PPC_ENABLE_HCALL 104
 #define KVM_CAP_CHECK_EXTENSION_VM 105
+#define KVM_CAP_S390_USER_SIGP 106
 
 #ifdef KVM_CAP_IRQ_ROUTING