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Date: Mon, 25 Oct 2010 16:20:46 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: backdoor
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To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org

On 10/25/2010 08:37 AM, Lluís wrote:
> Paolo Bonzini writes:
>
>    
>> On 10/25/2010 12:54 PM, Lluís wrote:
>>      
>>> * Backdoor channels need to provide arguments.
>>> * It's better to provide the same mechanism for both *-user and softmmu
>>> (otherwise the application to simulate or the interposed librariy
>>> should be compiled differently on every case).
>>>        
>    
>> You can add the syscall and, if it returns with ENOSYS, fall back to MMIO/PIO
>> (you don't really need a special driver, only some chmod since BARs are
>> accessible from /sys) or watchpoint/breakpoint.
>>      
> That sounds nice, but would only work with Linux. I, for example, did
> some full-system simulations with a QNX guest.
>
> I know extending the ISA is not nice at all, but I think that's much
> more maintainable than a per-guest OS interface (supposing some will
> need extra guest drivers).
>    

On x86, there are some architecturally nicer ways to do this.

For instance, a CPUID leaf could be used in the 0x40001xxx range.

Regards,

Anthony Liguori