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Re: [Xen-devel] [PATCH] x86: fix feature availability for PV guests

To: Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] x86: fix feature availability for PV guests
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 14 Mar 2008 11:33:39 +0000
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On 14/3/08 11:28, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> PV guests should not be allowed to believe features not currently
> virtualized (in many cases, requiring special MSRs) are available. Of
> course it is bad enough that to work on older hypervisors guests will
> still need to special case this, but better fix it now than never.

IMO we should whitelist the features just as we now do for HVM guests. We
already have that code; although we probably cannot easily share it with the
PV code, it probably only needs copying-and-tweaking.

> A question I came across while doing this - why is is_pv_32bit_vcpu()
> not simply defined to constant 1 on 32-bits?

Because it is occasionally applied to HVM guests.

 -- Keir



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