Messages in this thread | | | Subject | Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure | From | Benjamin Herrenschmidt <> | Date | Wed, 30 Aug 2017 07:19:30 +1000 |
| |
On Tue, 2017-08-29 at 13:27 +0200, Peter Zijlstra wrote: > mpe helped me out and explained that is the PWC hint to TBLIE. > > So, you set need_flush_all when you unhook pud/pmd/pte which you then > use to set PWC. So free_pgtables() will do the PWC when it unhooks > higher level pages. > > But you're right that there's some issues, free_pgtables() itself > doesn't seem to use mm->page_table_lock,pmd->lock _AT_ALL_ to unhook the > pages. > > If it were to do that, things should work fine since those locks would > then serialize against the speculative faults, we would never install a > page if the VMA would be under tear-down and it would thus not be > visible to your caches either.
That's one case. I don't remember of *all* the cases to be honest, but I do remember several times over the past few years thinking "ah we are fine because the mm sem taken for writing protects us from any concurrent tree structure change" :-)
Cheers, Ben.
| |