Re: [PATCH 3/4] KVM: s390: replace bitmap_copy with bitmap_{from,to}_arr64 where appropriate

Yury Norov
2022-04-21T13:01:29Z

On Thu, Apr 21, 2022 at 09:24:20AM +0200, David Hildenbrand wrote:
> On 21.04.22 00:25, Yury Norov wrote:
> > Copying bitmaps from/to 64-bit arrays with bitmap_copy is not safe
> > in general case. Use designated functions instead.
> >
>
> Just so I understand correctly: there is no BUG, it's just cleaner to do
> it that way, correct?

Yes. there's no bug, but the pattern is considered bad.

https://lore.kernel.org/all/YiCWNdWd+AsLbDkp@smile.fi.intel.com/T/#m9080cbb8a8235d7d4b7e38292cee8e4903f9afe4q

> IIUC, bitmap_to_arr64() translates to bitmap_copy_clear_tail() on s390x.

Yes.

> As the passed length is always 1024 (KVM_S390_VM_CPU_FEAT_NR_BITS), we
> essentially end up with bitmap_copy() again.
>
>
> Looks cleaner to me

Thanks.

> Reviewed-by: David Hildenbrand <david@redhat.com>
>
>
> --
> Thanks,
>
> David / dhildenb