[uml-devel] [PATCH] uml: problem with 2G/2G host address space

[uml-devel] [PATCH] uml: problem with 2G/2G host address space

[Joris van Rantwijk]

Hello,

I believe the current version (2.6.16.2) of UML does not work properly
on a i386 host with non-3G/1G address space split. The included patch
attempts to fix this.

On a i386 2.6.16.2 host configured with "3G/1G user/kernel split for
full 1G low memory" (VMSPLIT_3G_OPT), I found that UML would crash
on boot with the following error message:
  mapping mmap stub failed, errno = 12

It soon made sense to me that a 3G/1G configured UML would crash like
this, but I then found that UML 2.6.16.2 configured for 2G/2G crashed
in exactly the same way. I think this is due to the fact that STUB_CODE
and STUB_DATA are fixed at the 3G/1G settings. After changing these
settings, everything seems to work properly in 2G/2G mode.

Bye,
  Joris.

diff -urN -U 5 linux-2.6.16.2/arch/um/Kconfig.i386 linux-2.6.16.2-joris/arch/um/Kconfig.i386
--- linux-2.6.16.2/arch/um/Kconfig.i386	2006-04-07 18:56:47.000000000 +0200
+++ linux-2.6.16.2-joris/arch/um/Kconfig.i386	2006-04-09 11:33:46.000000000 +0200
@@ -33,15 +33,17 @@
 	However, this it experimental on 32-bit architectures, so if unsure say
 	N (on x86-64 it's automatically enabled, instead, as it's safe there).
 
 config STUB_CODE
 	hex
-	default 0xbfffe000
+	default 0xbfffe000 if !HOST_2G_2G
+	default 0x7fffe000 if HOST_2G_2G
 
 config STUB_DATA
 	hex
-	default 0xbffff000
+	default 0xbffff000 if !HOST_2G_2G
+	default 0x7ffff000 if HOST_2G_2G
 
 config STUB_START
 	hex
 	default STUB_CODE
 
--


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Re: [uml-devel] [PATCH] uml: problem with 2G/2G host address space

[Jeff Dike]

On Sun, Apr 09, 2006 at 12:57:55PM +0200, Joris van Rantwijk wrote:
> It soon made sense to me that a 3G/1G configured UML would crash like
> this, but I then found that UML 2.6.16.2 configured for 2G/2G crashed
> in exactly the same way. I think this is due to the fact that STUB_CODE
> and STUB_DATA are fixed at the 3G/1G settings. After changing these
> settings, everything seems to work properly in 2G/2G mode.

Your analysis is correct, and the patch is fine as far as it goes, but
we were talking about this a week or so ago about detecting the host
address space split at runtime.  There's a lot more potential
flexibility there than just 3/1 and 2/2.

				Jeff


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Re: [uml-devel] [PATCH] uml: problem with 2G/2G host address space

[Blaisorblade]

On Sunday 09 April 2006 19:01, Jeff Dike wrote:
> On Sun, Apr 09, 2006 at 12:57:55PM +0200, Joris van Rantwijk wrote:
> > It soon made sense to me that a 3G/1G configured UML would crash like
> > this, but I then found that UML 2.6.16.2 configured for 2G/2G crashed
> > in exactly the same way. I think this is due to the fact that STUB_CODE
> > and STUB_DATA are fixed at the 3G/1G settings. After changing these
> > settings, everything seems to work properly in 2G/2G mode.

> Your analysis is correct, and the patch is fine as far as it goes, but
> we were talking about this a week or so ago about detecting the host
> address space split at runtime.  There's a lot more potential
> flexibility there than just 3/1 and 2/2.

Jeff, for now please merge a band-aid patch (and also add an option to support 
1G/3G, while at it).

Delaying the band-aid only makes sense when you've got the proper fix reaching 
completion or when the band-aid is clearly an hack and hinders maintenability 
in a relevant way - we don't want to keep these configurations "unsupported".

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade


	

	
		
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Re: [uml-devel] [PATCH] uml: problem with 2G/2G host address space

[Jeff Dike]

On Wed, Apr 19, 2006 at 11:52:00AM +0200, Blaisorblade wrote:
> Jeff, for now please merge a band-aid patch (and also add an option
> to support 1G/3G, while at it).

OK, do you have such a patch handy?  I know I saw one go by, but some
grepping didn't turn it up.

				Jeff


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Re: [uml-devel] [PATCH] uml: problem with 2G/2G host address space

[Jeff Dike]

On Tue, Apr 25, 2006 at 04:19:22PM -0400, Jeff Dike wrote:
> OK, do you have such a patch handy?  I know I saw one go by, but some
> grepping didn't turn it up.

Nevermind, I found it - it was the start of this thread.

				Jeff


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