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RE: [Xen-devel] [PATCH] Implement rdtscp emulation and rdtscp_aux "suppo

To: "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] Implement rdtscp emulation and rdtscp_aux "support"
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Thu, 26 Nov 2009 15:23:16 +0000
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>>> Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> 26.11.09 15:57 >>>
>I suppose it's a moot point since Keir has patched it already
>anyway, but what is the mechanism for Linux to do this?
>Have you tried it on SuSE or any recent distro lately?
>Does Linux emulate rdtsc then (and, if so, could you point
>me to the code in the kernel that does it)?
>I ask because I found that the dynamic loader uses rdtsc
>(harmlessly) so if CR4.TSD is turned off by Linux and
>Linux doesn't emulate rdtsc, I suspect turning on this
>security option is suicidal.

I didn't try it, I just know the code is there. See
arch/x86/kernel/process.c for its handling of TIF_NOTSC, settable
through sys_prctl(PR_SET_TSC, ...).


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