Re: [PATCH V15] mm/debug: Add tests validating architecture page table helpers

[Qian Cai]

> On Mar 6, 2020, at 7:03 PM, Anshuman Khandual <Anshuman.Khandual@xxxxxxx> wrote:
> 
> Hmm, set_pte_at() function is not preferred here for these tests. The idea
> is to avoid or atleast minimize TLB/cache flushes triggered from these sort
> of 'static' tests. set_pte_at() is platform provided and could/might trigger
> these flushes or some other platform specific synchronization stuff. Just

Why is that important for this debugging option?

> wondering is there specific reason with respect to the soft lock up problem
> making it necessary to use set_pte_at() rather than a simple WRITE_ONCE() ?

Looks at the s390 version of set_pte_at(), it has this comment,
vmaddr);

/*
 * Certain architectures need to do special things when PTEs
 * within a page table are directly modified.  Thus, the following
 * hook is made available.
 */

I can only guess that powerpc  could be the same here.