Re: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
> Paul Durrant
> Sent: 07 June 2017 11:37
> To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; 'Juergen Gross'
> <jgross@xxxxxxxx>; Jan Beulich <JBeulich@xxxxxxxx>
> Cc: xen-devel (xen-devel@xxxxxxxxxxxxxxxxxxxx) <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>; Julien Grall (julien.grall@xxxxxxx)
> <julien.grall@xxxxxxx>; 'Boris Ostrovsky' <boris.ostrovsky@xxxxxxxxxx>
> Subject: Re: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot
> 
> > -----Original Message-----
> [snip]
> > >>
> > >> TBH: I really can't see what is wrong with that patch. The only change
> > >> which should be able to break something seems to be the reduction of
> > the
> > >> wakeup stack size to 3kB, but this shouldn't affect booting the system
> > >> at all...
> > >>
> > > Yeah, my next test is going to be increasing the size of the wakeup stack
> > again, but there is really nothing obviously wrong with the patch.
> >
> > My gut feeling is that there is some path through boot (tickled by these
> > two machines) which is clobbering the wrong piece of memory, which was
> > previously safe and is now not, because of the rearrangements here.
> >
> > Debugging these machines is very tricky, because they have no serial or
> > IMPI whatsoever.
> >
> 
> It does appear to be a layout issue. If I modify the code to just set
> wakeup_stack to wakeup_stack_start + PAGE_SIZE, so it has the full 4k then I
> still get the problem. However if I then move that code block that includes
> wakeup.S and move it to the end of trampoline.S so that wakup code and
> stack are once again located at the end then the problem goes away.
> 

It appears that it is just the code that needs to go at the end. The following 
patch is sufficient to avoid the problem. This may be preferable to a full 
reversion...

  Paul

diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 4d640f3fcd..7709a782f9 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -156,7 +156,7 @@ start64:
         movabs  $__high_start,%rax
         jmpq    *%rax

-#include "wakeup.S"
+ENTRY(wakeup_stack_start)

 /* The first page of trampoline is permanent, the rest boot-time only. */
 /* Reuse the boot trampoline on the 1st trampoline page as stack for wakeup. */
@@ -280,3 +280,4 @@ rm_idt: .word   256*4-1, 0, 0
 #include "mem.S"
 #include "edd.S"
 #include "video.S"
+#include "wakeup.S"
diff --git a/xen/arch/x86/boot/wakeup.S b/xen/arch/x86/boot/wakeup.S
index f9632eef95..d4824b55d5 100644
--- a/xen/arch/x86/boot/wakeup.S
+++ b/xen/arch/x86/boot/wakeup.S
@@ -173,5 +173,3 @@ bogus_saved_magic:
         movw    $0x0e00 + 'S', 0xb8014
         jmp     bogus_saved_magic

-/* Stack for wakeup: rest of first trampoline page. */
-ENTRY(wakeup_stack_start)

>   Paul
> 
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