On 2020-05-31 00:04, Souptick Joarder wrote: ...
+/* + * pin_user_pages_locked() is the FOLL_PIN variant of get_user_pages_locked(). + * Behavior is the same, except that this one sets FOLL_PIN and rejects + * FOLL_GET. + */ +long pin_user_pages_locked(unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + int *locked) +{ + /* + * FIXME: Current FOLL_LONGTERM behavior is incompatible with + * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on + * vmas. As there are no users of this flag in this call we simply + * disallow this option for now. + */ + if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM)) + return -EINVAL; + + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN;Right now get_user_pages_locked() doesn't have similar check for FOLL_PIN
Yes, that should be added...
and also not setting FOLL_GET internally irrespective of gup_flags passed by user. Do we need to add the same in get_user_pages_locked() ?
...and no, that should not. Yes, it's prudent to assert that FOLL_PIN is *not* set, at all the get_user_pages*() API calls, thanks for spotting that. I'll add that to this patch and send out a v2. The same check should also be added to get_user_pages_unlocked(). I'll send out a correction (I think just a v3 of that patchset) to add that. The setting of FOLL_GET, on the other hand, is something best left as-is so far. Some call sites set FOLL_GET, some want it *not* set, and some expect that FOLL_GET is implied, and at the moment, the delicate balance is correct. :) thanks, -- John Hubbard NVIDIA
