On 02/07/2018 12:46 PM, David Hildenbrand wrote:
> 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@xxxxxxxxxx>
> ---
> arch/s390/kvm/kvm-s390.c | 32 +++++++++++++++++++++++++++++---
> 1 file changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d007b737cd4d..c2b62379049e 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -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)
> +{
> + u64 delta_idx = 0;
we only add it to epdx, so should it be u8?
> +
> + /*
> + * 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 = 0xff;
and -1 then here?
> +
> + scb->epoch += delta;
> + if (scb->ecd & ECD_MEF) {
> + scb->epdx += delta_idx;
> + if (scb->epoch < delta)
> + scb->epdx += 1;
