linux-kernel - Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support

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Date:	Thu, 26 Jun 2008 12:02:49 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	xen-devel <xen-devel@...ts.xensource.com>,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Nick Piggin <npiggin@...e.de>,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support

Ingo Molnar wrote:
> that fixed the build but now we've got a boot crash with this config:
>
>  time.c: Detected 2010.304 MHz processor.
>  spurious 8259A interrupt: IRQ7.
>  BUG: unable to handle kernel NULL pointer dereference at  0000000000000000
>  IP: [<0000000000000000>]
>  PGD 0
>  Thread overran stack, or stack corrupted
>  Oops: 0010 [1] SMP
>  CPU 0
>   

I don't know if this will fix this bug, but it's definitely a bugfix.  
It was trashing random pages by overwriting them with pagetables...

Subject: x86_64: memory mapping: don't trash large pmd mapping

Don't trash a large pmd's data when mapping physical memory.
This is a bugfix for "x86_64: adjust mapping of physical pagetables
to work with Xen".

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/mm/init_64.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

===================================================================
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -311,7 +311,8 @@
 		}
 
 		if (pmd_val(*pmd)) {
-			phys_pte_update(pmd, address, end);
+			if (!pmd_large(*pmd))
+				phys_pte_update(pmd, address, end);
 			continue;
 		}
 


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