KVM: s390: switch to get_tod_clock() and fix STP sync races

Nobody except early.c makes use of store_tod_clock() to handle the
cc. So if we would get a cc != 0, we would be in more trouble.

Let's replace all users with get_tod_clock(). Returning a cc
on an ioctl sounded strange either way.

We can now also easily move the get_tod_clock() call into the
preempt_disable() section. This is in fact necessary to make the
STP sync work as expected. Otherwise the host TOD could change
and we would end up with a wrong epoch calculation.

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

2 files changed, 6 insertions, 20 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 0a67c40eece9..a0907795f31d 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -523,19 +523,14 @@ static int kvm_s390_set_tod_low(struct kvm *kvm, struct kvm_device_attr *attr)
 {
         struct kvm_vcpu *cur_vcpu;
         unsigned int vcpu_idx;
-        u64 host_tod, gtod;
-        int r;
+        u64 gtod;
 
         if (copy_from_user(&gtod, (void __user *)attr->addr, sizeof(gtod)))
                 return -EFAULT;
 
-        r = store_tod_clock(&host_tod);
-        if (r)
-                return r;
-
         mutex_lock(&kvm->lock);
         preempt_disable();
-        kvm->arch.epoch = gtod - host_tod;
+        kvm->arch.epoch = gtod - get_tod_clock();
         kvm_s390_vcpu_block_all(kvm);
         kvm_for_each_vcpu(vcpu_idx, cur_vcpu, kvm)
                 cur_vcpu->arch.sie_block->epoch = kvm->arch.epoch;
@@ -581,15 +576,10 @@ static int kvm_s390_get_tod_high(struct kvm *kvm, struct kvm_device_attr *attr)
 
 static int kvm_s390_get_tod_low(struct kvm *kvm, struct kvm_device_attr *attr)
 {
-        u64 host_tod, gtod;
-        int r;
-
-        r = store_tod_clock(&host_tod);
-        if (r)
-                return r;
+        u64 gtod;
 
         preempt_disable();
-        gtod = host_tod + kvm->arch.epoch;
+        gtod = get_tod_clock() + kvm->arch.epoch;
         preempt_enable();
         if (copy_to_user((void __user *)attr->addr, &gtod, sizeof(gtod)))
                 return -EFAULT;
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index 4d21dc4d1a84..b253de5b8945 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -34,7 +34,7 @@
 static int handle_set_clock(struct kvm_vcpu *vcpu)
 {
         struct kvm_vcpu *cpup;
-        s64 hostclk, val;
+        s64 val;
         int i, rc;
         ar_t ar;
         u64 op2;
@@ -49,15 +49,11 @@ static int handle_set_clock(struct kvm_vcpu *vcpu)
         if (rc)
                 return kvm_s390_inject_prog_cond(vcpu, rc);
 
-        if (store_tod_clock(&hostclk)) {
-                kvm_s390_set_psw_cc(vcpu, 3);
-                return 0;
-        }
         VCPU_EVENT(vcpu, 3, "SCK: setting guest TOD to 0x%llx", val);
-        val = (val - hostclk) & ~0x3fUL;
 
         mutex_lock(&vcpu->kvm->lock);
         preempt_disable();
+        val = (val - get_tod_clock()) & ~0x3fUL;
         kvm_for_each_vcpu(i, cpup, vcpu->kvm)
                 cpup->arch.sie_block->epoch = val;
         preempt_enable();