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xen-devel
[Xen-devel] Re: [PATCH][RFC] Emulating real mode with x86_emulate
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To: |
"Anthony Liguori" <aliguori@xxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH][RFC] Emulating real mode with x86_emulate |
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From: |
"Kamble, Nitin A" <nitin.a.kamble@xxxxxxxxx> |
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Date: |
Mon, 2 Apr 2007 16:52:25 -0700 |
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Cc: |
"Yu, Wilfred" <wilfred.yu@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx> |
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Mon, 02 Apr 2007 16:51:21 -0700 |
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[PATCH][RFC] Emulating real mode with x86_emulate |
On Mon, 2007-04-02 at 11:54 -0700, Anthony Liguori wrote:
Before calling x86_emulate, we use hvm_store_cpu_guest_regs() to copy
the guest state into a regs struct (which happens to be the vcpu's reg
struct). This reads directly from the VMCS via vmread() so it should be
okay. I don't think a vmx_world_save/restore is actually needed
although perhaps I'm missing something?
It may be ok to use hvm_store_cpu_guest_regs() for 1st few instructions, but I think it is not complete enough for emulator use.
> Also the function arch_vmx_do_resume() is called at the time of vcpu
> schedule, so it is not right to call the vmx_do_emulate() from there.
Right, the idea was to have x86_emulate() be called instead of
vmentry(). I thought that being in the set_cr0 path would ensure that
we go through do_resume() again. Is this assumption incorrect?
Yes, This assumption is not right. arch_vmx_do_resume() is assigned to schedule tail, so that the vcpu context is saved/restored when another vcpu is scheduled on the physical cpu.
I didn't want to just stick it in the set_cr0 path because we ought to
be able to pull the emulation loop into common code for SVM/VT and the
do_resume path seems like the only place where there's common place to
hook right now.
I thought the emulator will be needed only for VMX; why is it needed for SVM?
Also calling the x86_emulate() to emulate multiple instructions from vmx_do_resume() will block the physical cpu from other vcpus.
I think we discussed the approach of using the non-root context for for emulator within the Xen. Or did I misunderstanding it?
Regards,
Anthony Liguori
Thanks & Regards,
Nitin
Open Source Technology Center, Intel Corporation.
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