x86/paravirt: groundwork for 64-bit Xen support, fix #2

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...

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@citrix.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Cc: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 5c3305e05078..b10b7f17ea58 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -320,7 +320,8 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end)
                 }
 
                 if (pmd_val(*pmd)) {
-                        phys_pte_update(pmd, address, end);
+                        if (!pmd_large(*pmd))
+                                phys_pte_update(pmd, address, end);
                         continue;
                 }