linux-kernel - Re: [PATCH] x86: export 'pcibios

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Message-ID: <20120322004135.GA4253@udknight>
Date:	Thu, 22 Mar 2012 08:41:35 +0800
From:	Wang YanQing <udknight@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Michal Januszewski <spock@...too.org>,
	linux-fbdev@...r.kernel.org, x86@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86: export 'pcibios_enabled'

On Wed, Mar 14, 2012 at 11:21:37AM +0000, Alan Cox wrote:
> You can use set_memory_x() to mark memory executable (and _nx to set it back).
> 
NO I can't, if I set_memory_x and don't set pcibios_enabled = 1, then
static_protections will still failed because pcibios_enabled == 0, 
and I don't want to use set_memory_x, because I don't want to give the user 
of uvesafb that feeling "I will lost BIOS NX protection if I choice uvesafb."

> If you really need to know if NX is being used then the check
> 
> 	if (__supported_pte_mask & PTE_NX)
> 
> will do the trick and the variable is exported.
I don't understand what do you mean, do you means CONFIG_X86_PAE for 32? Or CONFIG_X86_64?
when NX is being used, the pci bios is NX or not also depend on
ACPI.ACPI on or off all will influnce the code path in pci_arch_init,
decide the set_bios_x have chance to execute or not.See
https://lkml.org/lkml/2011/11/16/84

By the way _PAGE_NX instead of PTE_NX, right?

> I'd suggest however you wrap that in a cpu_has_nx() type macro somewhere
> in the arch headers.
> 
The same above.

> If you go poking around pcibios values you are going to get burned if
> someone is ever bored enough to make NX and PCIBIOS work together
> differently.
> 
Indeed according to 5bd5a452662bc37c54fb6828db1a3faf87e6511c, who bring me 
the trouble, check the pcibios_enabled is the only simple and good way to 
resolve the Oops I meet.

If you really don't want it, and if I am not all wrong about your "helper method",
you means you want export the below:
int check_pcibios_enabled()?
See https://lkml.org/lkml/2012/2/26/124

Thanks.

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