linux-kernel - Re: [patch 0/4] x86: PAT followup - Incremental changes and bug fixes

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Message-ID: <20080117221505.GB18883@elte.hu>
Date:	Thu, 17 Jan 2008 23:15:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andreas Herrmann3 <andreas.herrmann3@....COM>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>, ak@....de,
	ebiederm@...ssion.com, rdreier@...co.com,
	torvalds@...ux-foundation.org, gregkh@...e.de, airlied@...net.ie,
	davej@...hat.com, tglx@...utronix.de, hpa@...or.com,
	akpm@...ux-foundation.org, arjan@...radead.org,
	jesse.barnes@...el.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/4] x86: PAT followup - Incremental changes and bug
	fixes


* Andreas Herrmann3 <andreas.herrmann3@....COM> wrote:

> On Thu, Jan 17, 2008 at 10:42:09PM +0100, Ingo Molnar wrote:
> > 
> > * Siddha, Suresh B <suresh.b.siddha@...el.com> wrote:
> > 
> > > On Thu, Jan 17, 2008 at 10:13:08PM +0100, Ingo Molnar wrote:
> > > > but in general we must be robust enough in this case and just degrade 
> > > > any overlapping page to UC (and emit a warning perhaps) - instead of 
> > > > failing the ioremap and thus failing the driver (and the bootup).
> > > 
> > > But then, this will cause an attribute conflicit. Old one was 
> > > specifying WB in PAT (ioremap with noflags) and the new ioremap 
> > > specifies UC.
> > 
> > we could fix up all aliases of that page as well and degrade them to UC?
> 
> Yes, we must fix all aliases or reject the conflicting mapping. But 
> fixing all aliases might not be that easy. (I've just seen a panic 
> when using your patch ;-(

yes, indeed my patch is bad if you have PAT enabled: conflicting cache 
attributes might be present. I'll go with your patch for now.

should we perhaps do UC by default for early_ioremap() as well? Normally 
those mappings are only temporary - but in case of a leak they might 
hang around in the pagetables and the CPU might stumble upon them. Also, 
should early_iounmap() do a wbinvd() [/clflush()] call as well, to be 
safe?

	Ingo
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