Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels

Sebastian Andrzej Siewior
2024-12-11T15:23:00Z

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.

> Yours,
> Linus Walleij

Sebastian