On Wed, Dec 11, 2024 at 4:22 PM Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > On 2024-12-11 14:29:29 [+0100], Linus Walleij wrote: > > So fast GUP is supposed to be lockless, and should just not > > have this problem. So it can't be addressing gup_fast_pgd_range() > > right? > … > > I'm more asking if HIGHPTE even acquires a spinlock anymore > > as it is supposed to be "fast"/lockless. If it does, it is clearly violating > > the "fast" promise of the fast GUP API and should not exist. > > This is lockless on x86. The problem is ARM's > arch_kmap_local_high_get(). This is where the lock is from. Aha that calls down to kmap_high_get() that that issues lock_kmap_any(flags). But is it really sound that the "fast" API does this? It feels like a violation of the whole design of the fast stuff. Yours, Linus Walleij
