Re: [PATCH] Fix i486 suspend to disk CR4 oops

From: Pavel Machek <pavel@suse.cz>
To: David Fries <david@fries.net>
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>,
	Ingo Molnar <mingo@elte.hu>,
	linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [PATCH] Fix i486 suspend to disk CR4 oops
Date: Tue, 19 Aug 2008 00:04:19 +0200	[thread overview]
Message-ID: <20080818220419.GB2053@elf.ucw.cz> (raw)
In-Reply-To: <20080818125803.GC17528@spacedout.fries.net>

On Mon 2008-08-18 07:58:03, David Fries wrote:
> On Mon, Aug 18, 2008 at 05:14:50AM +0100, Maciej W. Rozycki wrote:
> > On Sun, 17 Aug 2008, David Fries wrote:
> > > +	/* cr4 was introduced in the Pentium CPU */
> > 
> >  NACK.  Later i486 chips do have CR4 -- for PSE, VME, etc. (the set of
> > features varies across the line).  Use a fixup as elsewhere or something.

> 
> That's what I get for reading the Intel instruction set reference,
> "The CR4 register was added to the Intel Architecture beginning with
> the Pentium processor."
> 
> Ingo Molnar, thanks, I'll try the read_cr4_safe() version tonight (the
> computer is in the trunk of my car and I'm about ready to head to
> work).
> 
> In light of the above, how about updating the comments
> -       /* cr4 was introduced in the Pentium CPU */
> -       jecxz   1f      # cr4 Pentium and higher, skip if zero
> +       /* cr4 not in i386 only some i486, skip if zero */
> +       jecxz   1f      # cr4 not in i386 only some i486, skip if zero

Okay, can it happen that that cr4 is zero legitimately? If newer 486SX
chips support cr4 but not coprocessor...?
									Pavel
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