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Re: [Xen-devel] SMP on the MacBook

To: Marco Gerards <mgerards@xxxxxxxxx>
Subject: Re: [Xen-devel] SMP on the MacBook
From: gimli <gimli@xxxxxxxxxxxxxx>
Date: Thu, 10 Aug 2006 16:04:29 +0200
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I have xen running on my Macbook. The problem is cause by grub.
When i start the xen entry in grub with the key "return" xen
fails too boot. When i use the "Cursor key right" to start
the xen entry xen boots fine. I used the atached patch against
grub 0.97 for the Intel Macs.


Edgar (gimli) Hucek

Marco Gerards schrieb:
> Hi,
> For a while now I have been trying to debug an issue with Xen on the
> MacBook, doing this is part of my Summer of Code project to get Xen
> working properly on the Intel Mac.  In case some of you don't know,
> the MacBook is an Intel Core Duo based laptop from Apple, which lacks
> some legacy hardware.
> Xen (testing) works perfectly for me when starting it with "nosmp",
> however when not using it, it crashes while starting up the second
> core.  There have been some bug report on this issue already.
> Below I will explain the problem in more detail and with some
> observations.  I will be very grateful if someone can come up with
> ideas of how to fix this or give me some ideas that can lead to a
> solution.  Not only Xen has this problem, but so has FreeBSD and
> NetBSD, so a solution will be beneficial to these projects as well.
> What happens is the following: The first core sends two IPI
> messages(INIT and STARTUP) to start the second core.  When the second
> core is started, it notifies the first core of this so it can continue
> with the boot process.  However, the second core is not started by
> these messages, the loop that waits for the second core times out,
> continues and Xen crashes.
> One strange thing is that Xen initializes the second core properly
> when you press a key on the keyboard after the IPIs are sent.  I am
> expecting this interrupt somehow wakes up the second core so it can
> accept and process the IPIs.  Because it is a laptop the second core
> is put in deep sleep mode to save power in case an OS does not use
> this core at all.  But as I understand it, it should wake up when an
> INIT IPI arrives.
> The problems I am having with Xen can be reproduced with linux when
> booting with "acpi=ht", which means the ACPI interpreter is not
> started.
> Hopefully someone has some ideas how to deal with this issue and how
> to properly fix this.  If you want more information or want me to test
> things, feel free to ask.
> Thanks,
> Marco
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

--- grub-0.97.orig/stage2/asm.S 2004-06-19 18:55:22.000000000 +0200
+++ grub-0.97/stage2/asm.S      2006-04-21 11:10:52.000000000 +0200
@@ -1651,7 +1651,29 @@
        jnz     3f
-3:     /* use keyboard controller */
+3:     /*
+        * try to switch gateA20 using PORT92, the "Fast A20 and Init"
+        * register
+       */
+       mov $0x92, %dx
+       inb %dx, %al
+       /* skip the port92 code if it's unimplemented (read returns 0xff) */
+       cmpb $0xff, %al
+       jz 6f
+       /* set or clear bit1, the ALT_A20_GATE bit */
+       movb 4(%esp), %ah
+       testb %ah, %ah
+       jz 4f
+       orb $2, %al
+       jmp 5f
+4:     and $0xfd, %al
+       /* clear the INIT_NOW bit don't accidently reset the machine */
+5:     and $0xfe, %al
+       outb %al, %dx
+6:     /* use keyboard controller */
        pushl   %eax
        call    gloop1
@@ -1661,9 +1683,12 @@
        inb     $K_STATUS
+       cmpb    $0xff, %al
+       jz      gloopint1_done
        andb    $K_IBUF_FUL, %al
        jnz     gloopint1
        movb    $KB_OUTPUT_MASK, %al
        cmpb    $0, 0x8(%esp)
        jz      gdoit
@@ -1684,6 +1709,8 @@
        inb     $K_STATUS
+       cmpb    $0xff, %al
+       jz      gloop2ret
        andb    $K_IBUF_FUL, %al
        jnz     gloop1
@@ -1991,6 +2018,11 @@
        push    %ebp
+       call    EXT_C(console_checkkey)
+       incl    %eax
+       jz      wait_for_key
        call    EXT_C(prot_to_real)
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