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[Xen-devel] Re: [PATCH][RFC] Emulating real mode with x86_emulate

To: Andi Kleen <andi@xxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH][RFC] Emulating real mode with x86_emulate
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Fri, 30 Mar 2007 17:00:54 -0500
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
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Andi Kleen wrote:
There are some hard problems with migrating into QEMU. Namely, the code that QEMU generates isn't SMP safe (atomic instructions lose their atomicity)

I see.

You're worrying that real mode startup trampolines of OS rely on atomic instructions? I can't think of much other possible real mode
multi CPU code.

No, that's a concern for using V2E to handle 32 bit code. The big problem for handling real mode code is dealing with synchronization for device state. With the devices split between QEMU and within the hypervisor, this becomes even more complicated.

Any of the interesting guests that use big real mode also depend on being able to synchronize this device state.


Anthony Liguori


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