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Re: [Xen-devel] [PATCH] Implement rdtscp emulation and rdtscp_aux "supp

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Implement rdtscp emulation and rdtscp_aux "support"
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 26 Nov 2009 10:50:33 +0000
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 26/11/2009 10:26, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>> I'll fix this. While I'm at it, I think our PV emulation of MOV CR4,reg is
>> broken -- should just return v->arch.guest_context.ctrlreg[4], would you
>> agree? Otherwise guest's CR4.TSD isn't returned.
> Indeed, with the real bit no longer necessarily being in sync with the
> guest specified one simply reading the physical register doesn't work
> anymore. I'm somewhat uncertain about returning
> v->arch.guest_context.ctrlreg[4] though, since there should have
> been a reason we used the more expensive read of the real register
> (but looking at the code I can't determine that hypothetical reason).

I expect it's old code which predates things like pv_guest_cr4_fixup().
Since you can't see any reason why we should use read_cr4() either these
days, I'll change it.

 -- Keir

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