On Fri, Nov 20, 2020 at 04:00:23PM +0100, Peter Zijlstra wrote:
> On Fri, Nov 20, 2020 at 02:35:55PM +0000, Will Deacon wrote:
> > Since commit 0758cd830494 ("asm-generic/tlb: avoid potential double flush"),
> > TLB invalidation is elided in tlb_finish_mmu() if no entries were batched
> > via the tlb_remove_*() functions. Consequently, the page-table modifications
> > performed by clear_refs_write() in response to a write to
> > /proc/<pid>/clear_refs do not perform TLB invalidation. Although this is
> > fine when simply aging the ptes, in the case of clearing the "soft-dirty"
> > state we can end up with entries where pte_write() is false, yet a
> > writable mapping remains in the TLB.
> >
> > Fix this by calling tlb_remove_tlb_entry() for each entry being
> > write-protected when cleating soft-dirty.
> >
>
> > @@ -1053,6 +1054,7 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
> > ptent = pte_wrprotect(old_pte);
> > ptent = pte_clear_soft_dirty(ptent);
> > ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent);
> > + tlb_remove_tlb_entry(tlb, pte, addr);
> > } else if (is_swap_pte(ptent)) {
> > ptent = pte_swp_clear_soft_dirty(ptent);
> > set_pte_at(vma->vm_mm, addr, pte, ptent);
>
> Oh!
>
> Yesterday when you had me look at this code; I figured the sane thing
> to do was to make it look more like mprotect().
Ah, so you mean ditch the mmu_gather altogether?
> Why did you chose to make it work with mmu_gather instead? I'll grant
> you that it's probably the smaller patch, but I still think it's weird
> to use mmu_gather here.
>
> Also, is tlb_remote_tlb_entry() actually correct? If you look at
> __tlb_remove_tlb_entry() you'll find that Power-Hash-32 will clear the
> entry, which might not be what we want here, we want to update the
> entrty.
Hmm, I didn't spot that, although ptep_modify_prot_start() does actually
clear the pte so we could just move this up a few lines.
Will
>
>
>
