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From: "Yang, Bin" <bin.yang@intel.com>
To: "tglx@linutronix.de" <tglx@linutronix.de>
Cc: "mingo@kernel.org" <mingo@kernel.org>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"Gross, Mark" <mark.gross@intel.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"Hansen, Dave" <dave.hansen@intel.com>
Subject: Re: [PATCH v3 1/5] x86/mm: avoid redundant checking if pgprot has no change
Date: Tue, 4 Sep 2018 09:22:19 +0000	[thread overview]
Message-ID: <b75b65e3fe222fc927ee8e7379d5760d4cdafe8b.camel@intel.com> (raw)
In-Reply-To: <2db43c762164cada1b85ffd63262b5247fd2e3dc.camel@intel.com>

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

  reply	other threads:[~2018-09-04  9:22 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-21  1:16 [PATCH v3 0/5] x86/mm: fix cpu stuck issue in __change_page_attr_set_clr Bin Yang
2018-08-21  1:16 ` [PATCH v3 1/5] x86/mm: avoid redundant checking if pgprot has no change Bin Yang
2018-09-03 21:57   ` Thomas Gleixner
2018-09-04  7:01     ` Yang, Bin
2018-09-04  7:49       ` Thomas Gleixner
2018-09-04  9:12         ` Yang, Bin
2018-09-04  9:22           ` Yang, Bin [this message]
2018-08-21  1:16 ` [PATCH v3 2/5] x86/mm: avoid static_protection() checking if not whole large page attr change Bin Yang
2018-08-21  1:16 ` [PATCH v3 3/5] x86/mm: add help function to check specific protection flags in range Bin Yang
2018-09-03 22:10   ` Thomas Gleixner
2018-09-04  6:22     ` Yang, Bin
2018-08-21  1:16 ` [PATCH v3 4/5] x86/mm: optimize static_protection() by using overlap() Bin Yang
2018-09-04 12:22   ` Thomas Gleixner
2018-09-07  1:14     ` Yang, Bin
2018-09-07  7:49       ` Thomas Gleixner
2018-09-07  8:04         ` Yang, Bin
2018-09-07  8:21           ` Thomas Gleixner
2018-09-07  8:26             ` Yang, Bin
2018-08-21  1:16 ` [PATCH v3 5/5] x86/mm: add WARN_ON_ONCE() for wrong large page mapping Bin Yang
2018-09-03 22:27   ` Thomas Gleixner
2018-09-04  6:32     ` Yang, Bin
2018-09-04  7:41       ` Thomas Gleixner
2018-09-04 16:52         ` Thomas Gleixner
2018-09-07  2:12           ` Yang, Bin

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