linux-kernel - Re: [PATCH] video:uvesafb: Fix oops that uvesafb try to execute NX-protected page

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Date:	Wed, 28 Mar 2012 08:52:38 +0800
From:	Wang YanQing <udknight@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	FlorianSchandinat@....de, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, spock@...too.org
Subject: Re: [PATCH] video:uvesafb: Fix oops that uvesafb try to execute
 NX-protected page

On Tue, Mar 27, 2012 at 02:32:43PM +0100, Alan Cox wrote:
> On Tue, 27 Mar 2012 18:01:36 +0800
> Wang YanQing <udknight@...il.com> wrote:
> 
> > 
> > Ok! I try to check pcibios_enabled first, but get some opposition by Alan Cox,
> > but I want to make thing work and fix the oops, so I choice the simple way to
> > check the (__supported_pte_mask & _PAGE_NX) instead of to check this variable plus
> > pci kernel boot parameter, pci mmconfig works or not, and more, and more. It is not
> > the best method, but it works and maybe all will feel happy.
> 
> Okay let me ask the obvious question - why is it not the best method ?
> 
> Apart from adding a helper in the includes for the arch code of
> 
> 	static inline is_nx_enabled(void)
> 	{
> 		return !!(__supported_pte_mask & _PAGE_NX);
> 	}
> 
> is there anything else it lacks ?
> 
> Yes ideally we'd set the relevant ROM areas executable, but for a simple
> fix is there anything else that's a problem with it ?
Ok! Maybe you had missed my previous reply
http://permalink.gmane.org/gmane.linux.kernel/1272433
It is not the best method, because the check is not enough.
I means when NX is actively, the pci bios is NX or not also depend on
the code path in pci_arch_init which will be influenced by the acpi on or off, pci kernel boot
parameter, even kernel config like pci access method PCI_GOANY, PCI_GOMMCONFIG, or PCI_GODIRECT,
but if I check the pcibios_enabled, all the above can be ignored.

if uvesafb use the PMI when PCI BIOS is X, it can get the better work efficience then use the redraw 
method as a fallback when do the panning.
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