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[Xen-devel] Re: [RFC PATCH 15/33] move segment checks to subarch

To: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [RFC PATCH 15/33] move segment checks to subarch
From: Zachary Amsden <zach@xxxxxxxxxx>
Date: Tue, 18 Jul 2006 04:28:01 -0700
Cc: Andrew Morton <akpm@xxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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Arjan van de Ven wrote:
On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote:
plain text document attachment (i386-segments)
We allow for the fact that the guest kernel may not run in ring 0.
This requires some abstraction in a few places when setting %cs or
checking privilege level (user vs kernel).

-       regs.xcs = __KERNEL_CS;
+       regs.xcs = get_kernel_cs();

Hi,

wouldn't this patch be simpler if __KERNEL_CS just became the macro that
currently is get_kernel_cs() for the XEN case? then code like this
doesn't need changing at all...

The tradeoff is that then you can't use __KERNEL_CS is assembler code, and it is used in entry.S to detect NMI / debug trap workarounds - which don't actually need to be paravirtualized, as it is easier to hide the nasty cases which cause those side effects.

Zach

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