From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: Is exposing shared_info to user-land secure?
Date: Fri, 01 Aug 2008 13:35:23 -0700
Message-ID: <4893738B.9060702@goop.org>
References: <C4B90575.1BBE5%keir.fraser@eu.citrix.com>
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To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: "dan.magenheimer@oracle.com" <dan.magenheimer@oracle.com>, "Xen-Devel (E-mail)" <xen-devel@lists.xensource.com>
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Keir Fraser wrote:
> I think it might be okay. One issue is that how to let the user-space
> process know what vcpu it is running on, so it can use the correct timestamp
> info in a way that is safe against preemption. Bear in mind that the user
> address space may be shared by multiple concurrent threads on different
> VCPUs! If you assume consistent-tsc across all CPUs then the task is easier,
> but I don't think we'll want to bake that assumption into guest kernels and
> their interface to user processes.
>   

x86-64 already exports the current cpu and nodeid in the limit of a gdt 
entry, so you can fetch it from userspace with lsl.

    J