Re: [kvm-devel] [PATCH] KVM: emulator: Only allow VMCALL/VMMCALL trapped by #UD

[Avi K. <av...@qu...>]

Dong, Eddie wrote:
>>>> If migration happens while rip is in the hypercall page, and if the
>>>>
>>>>         
>>> I didn't quit catch here. The source VM vCPU is in Qemu migration
>>> part, The target VM VCPU is always waiting for migration
>>> data/command. If you mean SMP case, all target VCPUs are in waiting
>>> for data/cmd, and I assume source VCPUs are all in Qemu known state,
>>> not? 
>>>
>>>
>>>
>>>       
>> I'm talking about the guest rip.  The guest is not aware of the
>> migration. 
>>
>> Suppose that on the last copy that the guest rip is
>> (hypercall_page_virt + 3).  This address might be in the middle of
>> some instruction on the 
>> hypercall page on the target machine.  You need to fix up rip and
>>     
>
> This depends on how the hypercall page instruction is generated.
> In Xen's construction, the code in hypercall page is exactly same
> between SVM & VMX except the VMCALL/VMMCALL instruction itself.
>
>   

If you make the assumption that the hypercall is a single 3-byte 
instruction, then you might as well patch it directly.  Of course it 
depends on Intel and AMD not reusing each other's opcodes.

-- 
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