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Date: Thu, 16 Jul 2009 17:01:28 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] [PATCH] omit 3DNOW! CPUID bits from qemu64 CPU model
Message-ID: <20090716160128.GF16461@shareable.org>
References: <1247748571-20326-1-git-send-email-andre.przywara@amd.com>
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To: Alexander Graf <agraf@suse.de>
Cc: Andre Przywara <andre.przywara@amd.com>, qemu-devel@nongnu.org

Alexander Graf wrote:
> 
> On 16.07.2009, at 14:49, Andre Przywara wrote:
> 
> >Since we recently do not disable 3DNOW! support anymore, we should
> >avoid setting the bits in the default qemu64 CPU model to ease
> >migration. TCG does not support it anyway and even AMD deprecates
> >it's usage nowadays.
> 
> TCG does not implement it but it was enabled in the qemu64 type? That  
> sounds like a serious bug people would have found before.

Almost nobody uses 3DNow! with a 64-bit guest, so it's not so
easy to notice.

But I've have expected people running 32-bit guests on a qemu64 CPU to
notice, even if it's just the prefetch instructions...  unless those
happen to overlap with NOPs on non-3DNow! hardware.  (I'm too lazy to check).

> I really think we should try and keep the "qemu64" type (TCG  
> capabilities) and the "kvm safe" type separate. IMHO the best scenario  
> would be a -cpu "safe" type, used as default, that is the common  
> dominator between KVM on VMX, KVM on SVM and TCG.

qemu32 => TCG 32-bit
qemu64 => TCG 64-bit

safe32 => common between KVM and TCG, 32-bit
safe64 => common between KVM and TCG, 64-bit

?

> That would also make it easier to know where to put other fancy  
> features like "SVM" :-)

Can't we use SVM emulation with TCG and KVM both?

-- Jamie