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Subject[PATCH 4.14 089/110] KVM: s390: consider epoch index on TOD clock syncs
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Hildenbrand <david@redhat.com>

commit 1575767ef3cf5326701d2ae3075b7732cbc855e4 upstream.

For now, we don't take care of over/underflows. Especially underflows
are critical:

Assume the epoch is currently 0 and we get a sync request for delta=1,
meaning the TOD is moved forward by 1 and we have to fix it up by
subtracting 1 from the epoch. Right now, this will leave the epoch
index untouched, resulting in epoch=-1, epoch_idx=0, which is wrong.

We have to take care of over and underflows, also for the VSIE case. So
let's factor out calculation into a separate function.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180207114647.6220-5-david@redhat.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: 8fa1696ea781 ("KVM: s390: Multiple Epoch Facility support")
Cc: stable@vger.kernel.org
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[use u8 for idx]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/kvm/kvm-s390.c | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -169,6 +169,28 @@ int kvm_arch_hardware_enable(void)
static void kvm_gmap_notifier(struct gmap *gmap, unsigned long start,
unsigned long end);

+static void kvm_clock_sync_scb(struct kvm_s390_sie_block *scb, u64 delta)
+{
+ u8 delta_idx = 0;
+
+ /*
+ * The TOD jumps by delta, we have to compensate this by adding
+ * -delta to the epoch.
+ */
+ delta = -delta;
+
+ /* sign-extension - we're adding to signed values below */
+ if ((s64)delta < 0)
+ delta_idx = -1;
+
+ scb->epoch += delta;
+ if (scb->ecd & ECD_MEF) {
+ scb->epdx += delta_idx;
+ if (scb->epoch < delta)
+ scb->epdx += 1;
+ }
+}
+
/*
* This callback is executed during stop_machine(). All CPUs are therefore
* temporarily stopped. In order not to change guest behavior, we have to
@@ -184,13 +206,17 @@ static int kvm_clock_sync(struct notifie
unsigned long long *delta = v;

list_for_each_entry(kvm, &vm_list, vm_list) {
- kvm->arch.epoch -= *delta;
kvm_for_each_vcpu(i, vcpu, kvm) {
- vcpu->arch.sie_block->epoch -= *delta;
+ kvm_clock_sync_scb(vcpu->arch.sie_block, *delta);
+ if (i == 0) {
+ kvm->arch.epoch = vcpu->arch.sie_block->epoch;
+ kvm->arch.epdx = vcpu->arch.sie_block->epdx;
+ }
if (vcpu->arch.cputm_enabled)
vcpu->arch.cputm_start += *delta;
if (vcpu->arch.vsie_block)
- vcpu->arch.vsie_block->epoch -= *delta;
+ kvm_clock_sync_scb(vcpu->arch.vsie_block,
+ *delta);
}
}
return NOTIFY_OK;

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