VMInquiry means (1) the get operation should not call back into JS, (2) it should not throw any exceptions (except for OutOfMemoryError or StackOverflowError which can be thrown at any time), or have any side effects that is observable from JS code. In this case, llint_slow_path_get_private_name() is just implementating PrivateFieldGet (https://tc39.es/proposal-class-fields/#sec-privatefieldget) and has no need to use VMInquiry.
Created attachment 404839 [details]
Created attachment 404841 [details]
Comment on attachment 404841 [details]
Thanks for the review. Landed in r264679: <http://trac.webkit.org/r264679>.