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Re: [Xen-devel] Question about hyper-threading of domains

To: Lars Roland <lroland@xxxxxxxxx>
Subject: Re: [Xen-devel] Question about hyper-threading of domains
From: Jacob Gorm Hansen <jacobg@xxxxxxx>
Date: Fri, 29 Apr 2005 13:10:36 -0700
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Lars Roland wrote:

Seans fair enough - Out of curiosity have you published these
measurements anywere ?

No nothing yet, apart from the iperf numbers posted previously to this list.

I previously stated that using small address spaces means giving up
driver isolation, but I think that with the right use of segments that
should not be necessary, so there is no trade-off with regards to isolation.

Could you explain a little further how excalty you plan to avoid this
- I have been digging into this myslef and It is not obvious to me how
this can be achived,

I have not implemented this, and perhaps I am not understanding the x86 docs correctly, but it seems I can set up and expands-down segment to confine dom0 to its allowed range of addresses (0xf0000000 - 0xfc000000). If that does not work, I can move dom0 to the range 0x0 - 0x0c000000, and use the segment base to move it to 0xf0000000. The latter approach will require that I fix up copy_from_user and friends inside Xen to take this into account, but that seems doable.

Yes please - I have the time (and hardware) to check this.

I will try to roll something up later today or tomorrow, before flying to Boston for NSDI.


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