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RE: [Xen-devel] trap/interrupt gate for hypercall

To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] trap/interrupt gate for hypercall
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Wed, 16 May 2007 11:17:54 +0800
Cc: "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
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Thread-topic: [Xen-devel] trap/interrupt gate for hypercall
>From: Keir Fraser [mailto:keir@xxxxxxxxxxxxx]
>Sent: 2007年5月15日 23:30
>Interrupt handlers save and restore segment registers. We could fault on
>reload of a segment register and lose the original segment register
> -- Keir

I saw one necessity by always using interrupt gate type, that 
restore_all_xen can be simplified without segment registers restore. 
Or else at least ds/es need be restored for restore_all_xen if interrupt
happens at entrance of hypercall (if by trap gate type). But I'm weak 
knowledge about the reason you list. What's the ability that hypercall 
handler can do while interrupt handler can't when reload of a 
problematic segment register? Anyway interrupt can also raise from 
guest context and interrupt handle also needs to tackle fault of 
reloading. Could you kindly give an example? :-)


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