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Date: Fri, 07 Nov 2008 10:40:39 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] kvm: sync registers?
References: <491416EA.30706@redhat.com> <49144ABA.1030606@codemonkey.ws>
	<200811071631.54494.paul@codesourcery.com>
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To: Paul Brook <paul@codesourcery.com>
Cc: qemu-devel@nongnu.org

Paul Brook wrote:
> On Friday 07 November 2008, Anthony Liguori wrote:
>   
>> Gerd Hoffmann wrote:
>>     
>>>   Hi,
>>>
>>> How does kvm sync registers between kernel and qemu env?
>>> I see there are kvm_arch_{get,put}_registers() functions in
>>> target-i386/kvm.c, but grep doesn't find a single call of them?
>>>       
>> Right now, it doesn't.  We should probably sync registers in the same
>> places that kvm-userspace does (gdbstubs, vmport, etc.).
>>
>> I tried to always sync registers on every exit but this causes boot to
>> fail. The same is true of kvm-userspace though and I've been meaning to
>> dig into why this is.
>>     
>
> Maybe due to do with inconsistencies between the segment register contents and 
> the descriptor tables? I know I've written code that relies on this feature.
>   

VT/SVM actually allow you to get at the descriptor tables/cache and we 
save/restore them in KVM.  I only see this issue if I always 
save/restore registers so it leads me to think it's something more subtle.

Regards,

Anthony Liguori

> Paul
>