linux-kernel - Re: 2.6.32 stalls as guest in virtualbox

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Date:	Sat, 30 Jan 2010 19:46:24 +0100
From:	Christoph Biedl <linux-kernel.bfrz@...chmal.in-ulm.de>
To:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.32 stalls as guest in virtualbox

Christoph Biedl wrote...

(...)

Christian Ehrhard gave me a lot of help understanding the kernel sides
of that issue, thanks for this.  Appearently virtualbox cannot
properly deal with the result of alternative_io in
arch/x86/include/asm/cmpxchg_32.h since this klugdy patch

--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -317,7 +317,7 @@ extern unsigned long long cmpxchg_486_u64(volatile void *, u64, u64);
        __typeof__(*(ptr)) __ret;                               \
        __typeof__(*(ptr)) __old = (o);                         \
        __typeof__(*(ptr)) __new = (n);                         \
-       alternative_io("call cmpxchg8b_emu",                    \
+       alternative_io("lock; cmpxchg8b (%%esi)",               \
                        "lock; cmpxchg8b (%%esi)" ,             \
                       X86_FEATURE_CX8,                         \
                       "=A" (__ret),                            \

fixes the problem, 

Unlike his findings described in
<http://marc.info/?l=linux-kernel&m=121545190107704&w=2>, the guest
does not crash but seems to run into a busy loop instead.

A acceptable workaround is selecting CONFIG_M686 (but not CONFIG_M586).

Now I guess this is rather something to virtualbox guys should take
care of, therefore I've opened a ticket there:
http://www.virtualbox.org/ticket/6100

    Christoph
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