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Commit 1575767e authored by David Hildenbrand's avatar David Hildenbrand Committed by Christian Borntraeger
Browse files

KVM: s390: consider epoch index on TOD clock syncs 



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: default avatarDavid Hildenbrand <david@redhat.com>
Message-Id: <20180207114647.6220-5-david@redhat.com>
Reviewed-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Fixes: 8fa1696e ("KVM: s390: Multiple Epoch Facility support")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
[use u8 for idx]
parent d16b52cb

arch/s390/kvm/kvm-s390.c

+29 −3
Original line number Diff line number Diff line
@@ -179,6 +179,28 @@ 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
@@ -194,13 +216,17 @@ static int kvm_clock_sync(struct notifier_block *notifier, unsigned long val, 
	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;