On Tue, 2018-09-04 at 18:52 +0200, Thomas Gleixner wrote: > On Tue, 4 Sep 2018, Thomas Gleixner wrote: > > On Tue, 4 Sep 2018, Yang, Bin wrote: > > > On Tue, 2018-09-04 at 00:27 +0200, Thomas Gleixner wrote: > > > > On Tue, 21 Aug 2018, Bin Yang wrote: > > > > > @@ -625,6 +625,7 @@ try_preserve_large_page(pte_t *kpte, unsigned > > > > > long address, > > > > > > > > > > psize = page_level_size(level); > > > > > pmask = page_level_mask(level); > > > > > + addr = address & pmask; > > > > > > > > > > /* > > > > > * Calculate the number of pages, which fit into this large > > > > > @@ -636,6 +637,12 @@ try_preserve_large_page(pte_t *kpte, unsigned > > > > > long address, > > > > > cpa->numpages = numpages; > > > > > > > > > > /* > > > > > + * The old pgprot should not have any protection bit. Otherwise, > > > > > + * the existing mapping is wrong already. > > > > > + */ > > > > > + WARN_ON_ONCE(needs_static_protections(old_prot, addr, psize, > > > > > old_pfn)); > > > > > > > > The check itself is fine, but it just emits a warning and goes on as if > > > > nothing happened. > > > > > > > > We really want to think about a proper way to fix that up without > > > > overhead > > > > for the sane case. > > > > > > could we change it as below? I think it should be safe to split large > > > page if current mapping is wrong already. > > > > > > if (needs_static_protections(old_prot, addr, psize, old_pfn)) { > > > WARN_ON_ONCE(1); > > > goto out_unlock; > > > } > > > > Sure, but what enforces the static protections on the pages which are not > > in the modified range of the current CPA call? Nothing. > > I looked deeper into that. For the PMD split it's rather trivial to do, but > a PUD split would require a horrible pile of changes as we'd have to remove > the protections from the new PMD first, go all the way back and rescan the > new PMDs whether they need to be split up further. But that needs a lot of > refactoring and I'm not sure if it's worth the trouble right now. > > As we haven't cared about that since CPA got introduced, I think we just do > the consistency check and warn. That's better what we have now and when it > ever triggers revisit it.
Is below check enough? if ((pgprot_val(old_prot) & _PAGE_PRESENT) && needs_static_protections(old_prot, addr, psize, old_pfn)) { WARN_ON_ONCE(1); } > > Thanks, > > tglx