On 20.02.2018 16:36, Christian Borntraeger wrote:
>
>
> 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?
Indeed, this should 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?
Yes, thanks!
>
>> +
>> + scb->epoch += delta;
>> + if (scb->ecd & ECD_MEF) {
>> + scb->epdx += delta_idx;
>> + if (scb->epoch < delta)
>> + scb->epdx += 1;
>
>
--
Thanks,
David / dhildenb
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