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Re: [Qemu-devel] [PATCH] omit 3DNOW! CPUID bits from qemu64 CPU model
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] [PATCH] omit 3DNOW! CPUID bits from qemu64 CPU model |
Date: |
Thu, 16 Jul 2009 17:01:28 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
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