Re: [PATCH] mm: pgtable: protect lockless kernel page table walks with RCU

[David CARLIER]

sure thing. Thanks !

On Fri, 12 Jun 2026 at 05:52, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Fri, Jun 12, 2026 at 05:38:27AM +0100, David Carlier wrote:
> > @@ -434,6 +434,14 @@ static void kernel_pgtable_work_func(struct work_struct *work)
> >       spin_unlock(&kernel_pgtable_work.lock);
> >
> >       iommu_sva_invalidate_kva_range(PAGE_OFFSET, TLB_FLUSH_ALL);
> > +
> > +     /*
> > +      * Lockless kernel page table walkers (ptdump, and any other user of
> > +      * walk_kernel_page_table_range_lockless()) dereference these pages
> > +      * under rcu_read_lock(). Wait for a grace period so no walker can
> > +      * still be reading a page we are about to free.
> > +      */
> > +     synchronize_rcu();
> >       list_for_each_entry_safe(pt, next, &page_list, pt_list)
> >               __pagetable_free(pt);
>
> synchronize_rcu() is rather expensive.  Can't you rcu-free the page
> tables instead?  There's an rcu head in struct page.