linux-kernel - Re: [discuss] 2.6.23-rc8-mm1, -rc7-mm1 kill audio on HP nx6325

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Date:	Wed, 26 Sep 2007 10:22:30 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Andi Kleen <ak@...e.de>,
	Takashi Iwai <tiwai@...e.de>,
	LKML <linux-kernel@...r.kernel.org>, discuss@...-64.org
Subject: Re: [discuss] 2.6.23-rc8-mm1, -rc7-mm1 kill audio on HP nx6325

On Wed, 2007-09-26 at 08:32 +0100, Jan Beulich wrote:
> >ioremap_nocache() does __ioremap(..., _PAGE_PCD);, then __ioremap() does
> >ioremap_page_range(..., _PAGE_PCD | other_stuff) That's one.
> >
> >__ioremap() then does ioremap_change_attr(..., _PAGE_PCD);.  That's two.
> >
> >So I _think_ we're setting _PAGE_PCD twice on those pte's?  Unclear.  The
> >implementation is rather different from i386, too.
> >
> >I dunno why __change_page_attr() failed though.  Perhaps this, in
> >change_page_attr_addr():
> >
> >		if (!kernel_map || pte_present(pfn_pte(0, prot))) {
> >
> >should be &&
> 
> Definitely not, and this code has been that way for a while.
> 
> I rather suspect this change
> 
> -	if (!kpte) return 0;
> +	if (!kpte)
> +		return -EINVAL;
> 
> to be the reason for the failure (and I had already sent a comment to this
> respect to Andi upon his review request).

This change exposes the problem. The question is why we do not have a
page table entry for the address, which was mapped right before that.

	tglx


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