Re: [Xen-devel] Support real-mode in Xen?

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

Hi, 

At 14:23 +0000 on 19 Jan (1263910997), Jun Koi wrote:
> I am wondering how Xen currently supports real mode? Is it what
> explained in below old slides, or we already went another way?
> 
> http://xen.org/files/summit_3/v2e-realmode-support-v2.pdf

No, it's not done that way - to the best of my knowledge we don't use
the CPU emulation in qemu-dm at all.  

AMD CPUs and very recent Intel CPUs support running in real-mode 
in non-root context, so don't need any special handling for realmode.

On older Intel CPUs, when the guest is in real mode, it runs in virtual
8086 mode in non-root context.  Instructions that can't be handled by
virtual 8086 mode are emulated by Xen's built-in x86_emulate.
(look for 'vmx_realmode' in xen/arch/x86/hvm/vmx/vmx.c)

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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