Re: [Xen-devel] 2.6.28 64-bit domU not booting

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Chris Lalancette wrote:
> Just to dig up this old thread: we've been seeing the same thing.  I *think* it
> comes down to the NX bit (or the lack thereof); on machines without NX, the
> early pagetable setup is trying to use the NX bit in the PTE flags, and the
> hypervisor is telling it to go away.  The Red Hat bugzilla entry that I've filed
> has more analysis:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=492523
>
> Valtteri, can you give the output of "cat /proc/cpuinfo | grep flags", so we can
> confirm that it's probably the same issue?
>
> And it looks like Ian Campbell actually posted a patch upstream
> (http://lkml.indiana.edu/hypermail/linux/kernel/0901.3/02668.html) that should
> fix this, but I don't see it in any of the upstream trees.  Ian, Jeremy, do you
> guys know what the status is there?  It would be good to get into 2.6.30, and
> probably backport to the stable trees as well.
>   
Hm, yes, it does seem to have got lost.  But I wonder if a simpler fix 
isn't just test for NX early and set __supported_pte_mask accordingly.  
Does this work?
   J

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Date: Fri, 27 Mar 2009 11:29:02 -0700
Subject: [PATCH] xen: set _PAGE_NX in __supported_pte_mask before pagetable 
construction

Many 32-bit and some 64-bit machines don't support the NX flag in ptes.
Check for NX before constructing the kernel pagetables.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 992be7f..f8c9e49 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -42,6 +42,7 @@
#include <asm/xen/hypervisor.h>
#include <asm/fixmap.h>
#include <asm/processor.h>
+#include <asm/proto.h>
#include <asm/msr-index.h>
#include <asm/setup.h>
#include <asm/desc.h>
@@ -1003,6 +1004,13 @@ asmlinkage void __init xen_start_kernel(void)

        __supported_pte_mask |= _PAGE_IOMAP;

+       /* Work out if we support NX */
+#ifdef CONFIG_X86_64
+       check_efer();
+#else
+       set_nx();
+#endif
+
        /* Don't do the full vcpu_info placement stuff until we have a
           possible map and a non-dummy shared_info. */
        per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];





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