Re: [PATCH bpf-next] arm64: mm: Complete the PTE store in ptep_try_set()

[Tejun Heo]

> Can this path actually loop, or is the deferred barrier guaranteed to be
> flushed before the faulting instruction is retried?

I don't know the arm64 paths well enough to say. What I can see is that
ptep_try_set() only runs as an apply_to_page_range() callback, and
apply_to_pte_range() brackets it with lazy_mmu_mode_enable()/disable(), with
the disable() flushing TIF_LAZY_MMU_PENDING before returning. The barriers
would land before the access is retried. It also looks like the same
queue_pte_barriers() path __set_pte() already uses. I'd defer to Catalin and
the arm64 folks on whether that actually closes the case.

Thanks.

--
tejun