On Mon, Nov 22, 2021, Paolo Bonzini wrote:
> list_replace_init cannot be used if the source is an empty list,
> because "new->next->prev = new" will overwrite "old->next":
>
> new old
> prev = new, next = new prev = old, next = old
> new->next = old->next prev = new, next = old prev = old, next = old
> new->next->prev = new prev = new, next = old prev = old, next = new
> new->prev = old->prev prev = old, next = old prev = old, next = old
> new->next->prev = new prev = old, next = old prev = new, next = new
>
> The desired outcome instead would be to leave both old and new the same
> as they were (two empty circular lists). Use list_cut_before, which
> already has the necessary check and is documented to discard the
> previous contents of the list that will hold the result.
>
> Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm/sev.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 21ac0a5de4e0..75955beb3770 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1613,8 +1613,7 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
> src->handle = 0;
> src->pages_locked = 0;
>
> - INIT_LIST_HEAD(&dst->regions_list);
> - list_replace_init(&src->regions_list, &dst->regions_list);
> + list_cut_before(&dst->regions_list, &src->regions_list, &src->regions_list);
Yeesh, that is tricky. A list_move_all() helper in list.h to do
list_cut_before(dst, src, src);
would be nice.
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> }
>
> static int sev_es_migrate_from(struct kvm *dst, struct kvm *src)
> --
> 2.27.0
>
>
