Re: [PATCH v3 5/5] x86/mm: add WARN_ON_ONCE() for wrong large page mapping

Yang, Bin
2018-09-04T06:33:05Z

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;
}

>
> Thanks,
>
> tglx