Re: [Qemu-devel] [PATCH 0/3] target-i386: Don't trigger "check" warnings by default in KVM mode

[Paolo Bonzini]

On 03/11/2015 18:41, Eduardo Habkost wrote:
> I just got a report from David that the lack of ABM on Sandy Bridge
> hosts will trigger the warning, too. I guess we don't want to require a
> Haswell CPU to run the default CPU model with KVM, so ABM would be
> disabled by default in KVM mode too.
> 
> We really should make the defaults different in TCG and KVM mode. The
> question is what to do about the TCG defaults in QEMU 2.5.
> 
> I propose we remove ABM and SSE4E from qemu64 in 2.5,

But if we do that for all machine types we break guest ABI for >=Haswell
on old machine types; if we do that for 2.5 only we get "-cpu check"
warnings on old machine types.

This is true even if we implement different defaults for KVM and TCG.
Should we disable "-cpu check" for old machine types (or do we already
do that)?  That would suck, but it would let us drop ABM and SSE4A from
the 2.4 machine type without much hassle.

> and implement a
> proper mechanism to have different KVM and TCG defaults after 2.5. We
> never pretended that qemu64 had all TCG-supported features enabled
> anyway: the last time the feature set of qemu64 was changed was in 2009
> (when we added ABM).

That's true.

Paolo