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

On Mar 6, 2020, at 7:03 PM, Anshuman Khandual [off-list ref] 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.