KVM: s390: Avoid potentially sleeping while atomic when zapping pages

KVM: s390: Avoid potentially sleeping while atomic when zapping pages

Factor out try_get_locked_pte(), which behaves similarly to
get_locked_pte(), but does not attempt to allocate missing tables and
performs a spin_trylock() instead of blocking.

The new function is also exported, since it will be used in other
patches.

If intermediate entries are missing, there can be no pte swap entry to
free, so it's safe to ignore them.

This avoids potentially sleeping while atomic.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260602142356.169458-4-imbrenda@linux.ibm.com>