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Re: [Qemu-ppc] [PATCH] RFC: powerpc: add PVR compatibility check

From: Paul Mackerras
Subject: Re: [Qemu-ppc] [PATCH] RFC: powerpc: add PVR compatibility check
Date: Tue, 5 Nov 2013 15:00:10 +1100
User-agent: Mutt/1.5.21 (2010-09-15)

On Mon, Nov 04, 2013 at 10:05:58AM +0100, Alexander Graf wrote:
> Yeah, we really need to check that guest vpcu == host vcpu for HV KVM.

In general I agree, but the one difficulty I see is that a check for
exact equality will interact badly with qemu's habit of picking a
specific processor version when the user specifies something general
like "POWER7".  So if the user does -cpu POWER7 on a machine with
(for example) a POWER7 v2.1 processor, but qemu arbitrarily picks the
PVR for POWER7 v2.3, then it will fail, which will be completely
puzzling to the user -- "I asked for POWER7, and it is a POWER7,
what's the problem??".

Maybe if the user asks for a non-specific processor type, and the
host's PVR matches the request, then qemu should take the host's PVR
rather than just picking some arbitrary processor version.


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