Re: [PATCH v3 1/5] x86/mm: avoid redundant checking if pgprot has no change

Yang, Bin
2018-09-04T09:22:24Z

On Tue, 2018-09-04 at 17:11 +0800, Bin Yang wrote:
> On Tue, 2018-09-04 at 09:49 +0200, Thomas Gleixner wrote:
> > On Tue, 4 Sep 2018, Yang, Bin wrote:
> > > On Mon, 2018-09-03 at 23:57 +0200, Thomas Gleixner wrote:
> > > >
> > > > The last patch which does the overlap check is equally broken:
> > >
> > > Sorry that I did not understand the broken of last patch.
> >
> > I meant 4/5 sorry. That's the one which introduces the overlap check and
> > does this:
> >
> > > > + /*
> > > > + * Ensure that the requested pgprot does not violate static protection
> > > > + * requirements.
> > > > + */
> > > > + new_prot = static_protections(req_prot, address,
> > > > + numpages << PAGE_SHIFT, pfn);
> > > >
> > > > It expands new_prot to the whole range even if the protections only
> > > > overlap. That should not happen in practice, but we have no checks for that
> > > > at all.
> > >
> > > Below code in patch #3 should cover this check. It will double check
> > > new_prot in whole large page range.
> >
> > Which is exactly what is wrong. Read again what I wrote.

It looks this new_prot might have less protection bits and always
passes the following check at the begin numpages. I think it can be
changed as below:

new_prot = static_protections(req_prot, address,
1, pfn);

By the way, I just sent a empty mail to you. I am so sorry for it.

> >
> > Thanks,
> >
> > tglx