linux-kernel - Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

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Date:	Mon, 28 Jan 2008 21:26:44 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ian Campbell <ijc@...lion.org.uk>,
	Mika Penttilä <mika.penttila@...umbus.fi>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

On Monday, 28 of January 2008, Pavel Machek wrote:
> Hi!
> 
> > > >  /*
> > > >   * Swap suspend & friends need this for resume because things like the intel-agp
> > > >   * driver might have split up a kernel 4MB mapping.
> > > >   */
> > > > -char __nosavedata swsusp_pg_dir[PAGE_SIZE]
> > > > +char swsusp_pg_dir[PAGE_SIZE]
> > > 
> > > thanks, applied.
> 
> Sorry, this is subtle and I've overlooked it before.
> 
> (I thought you were only changing ifdef).
> 
> Now you memcpy() over pg_dir when that pgdir is in use during swsusp
> resume.

It is not.  swsusp hasn't been using swsusp_pg_dir for several months.
Hence, the patch. :-)

> Granted, you memcpy() with same data that already are there, 
> but it may still do some funny effects.
> 
> Hmm, but same argument applies to lower levels of paging in 64-bit and
> PAE cases, and we still do that memcpy-over-active-pagetables there...
> :-(.

Actually, no.  We only do that with the kernel code mapping which should be
safe as long as TLBs are not flushed (and they aren't).

Thanks,
Rafael
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