The previous check returned -1 when any page within
[start, start+len) is unmapped, not when all are unmapped.
Cc: Warner Losh <imp@bsdimp.com>
Cc: Kyle Evans <kevans@freebsd.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Message-Id: <20230707204054.8792-11-richard.henderson@linaro.org>