It should be fine, as:
static void make_uffd_wp_pte(struct vm_area_struct *vma,
unsigned long addr, pte_t *pte)
{
pte_t ptent = ptep_get(pte);
#ifndef CONFIG_USERFAULTFD_
if (pte_present(ptent)) {
pte_t old_pte;
old_pte = ptep_modify_prot_start(vma, addr, pte);
ptent = pte_mkuffd_wp(ptent);
ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent);
} else if (is_swap_pte(ptent)) {
ptent = pte_swp_mkuffd_wp(ptent);
set_pte_at(vma->vm_mm, addr, pte, ptent);
} else { <----------------- this must be pte_none() already
set_pte_at(vma->vm_mm, addr, pte,
make_pte_marker(PTE_MARKER_UFFD_WP));
}
}
Indeed! Is pte_swp_mkuffd_wp() reasonable for pte markers? I rememebr
that we don't support multiple markers yet, so it might be good enough.
2) We get the error on arm64, which does *not* support uffd-wp. Do we
maybe end up calling make_uffd_wp_pte() and place a pte marker, even
though we don't have CONFIG_PTE_MARKER_UFFD_WP?
static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
{
#ifdef CONFIG_PTE_MARKER_UFFD_WP
return is_pte_marker_entry(entry) &&
(pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
#else
return false;
#endif
}
Will always return false without CONFIG_PTE_MARKER_UFFD_WP.
But make_uffd_wp_pte() might just happily place an entry. Hm.
The following might fix the problem:
[...]
I'd like to double check with Muhammad (as I didn't actually follow his
work in the latest versions.. quite a lot changed), but I _think_
fundamentally we missed something important in the fast path, and I think
it applies even to archs that support uffd..
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e91085d79926..3b81baabd22a 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2171,7 +2171,8 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
return 0;
}
- if (!p->vec_out) {
+ if (!p->vec_out &&
+ (p->arg.flags & PM_SCAN_WP_MATCHING))
Ouch, yes. So that's the global fence I was wondering where to find it.
--
Cheers,
David / dhildenb
