Message-ID: <47A7E8DF.3080209@linux.intel.com>
Date: Mon, 04 Feb 2008 20:41:03 -0800
From: Arjan van de Ven <arjan@linux.intel.com>
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To: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
CC: tglx@linutronix.de, mingo@elte.hu, linux-kernel@vger.kernel.org
Subject: Re: issue with patch "x86: no CPA on iounmap"
References: <20080205011357.GA14712@linux-os.sc.intel.com>
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Siddha, Suresh B wrote:
> This is wrt to x86 git commit f56d005d30342a45d8af2b75ecccc82200f09600
> 	"x86: no CPA on iounmap"
> 
> This can use performance issue. When a GART driver unmaps a RAM page,
> which was mapped as UC, this commit will still retain UC attribute
> on the kernel identity mapping. This can cause mysterious performance issue
> if this freed page gets used by kernel later.
> 
> For now we should change the attribute during iounmap and in future PAT
> infrastructure will have necessary hooks to avoid the aliasing issues.
> 

this is a hard one; because the flipside is someone ioremapping the same page twice
(which is not impossible if there's 2 1k bars)... and then one of them gets iounmapped,
which would turn the page cachable again.
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