Re: [Xen-devel] [Q] guest and user protection on x86-64 by paging

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

 On 08/01/2010 09:01 AM, Min Lee wrote:
> Hi, folks.
> one question. I'll read source code, but if one can give me brief 
> overview, it would be so helpful. On x86-64, guest and user runs both 
> in ring 3, and protect from each other by paging mechanism. but, how? 
> Then page table should be modified and TLB would be flushed for every 
> system call. This would be some overhead, I think. Is this what Xen is 
> doing?
Yes it is.  64-bit PV guests run at a considerable disadvantage.  The 
only mitigating factor is that it sets the Global bit on usermode ptes, 
so that they don't get flushed from tlb during the transition.
    J

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