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

[Paolo Bonzini <pbonzini@redhat.com>]

On 30/10/2015 20:13, Eduardo Habkost wrote:
> On Fri, Oct 30, 2015 at 05:00:57PM -0200, Eduardo Habkost wrote:
>> The x86 change to make "check" mode be enabled by default made QEMU print a
>> warning in the default case if running in an Intel host:
>>
>>   $ qemu-system-x86_64 -machine pc,accel=kvm
>>   warning: host doesn't support requested feature: CPUID.80000001H:ECX.sse4a [bit 6]
>>
>> Fix this by not enabling sse4a in qemu64 when in KVM mode.
>>
>> The long term solution will probably involve creating separate "tcg64" and
>> "kvm64" CPU models as defaults, so we can finally choose completely diffferent
>> defaults in the KVM- and TCG-specific models without making the
>> kvm_default_props list grow too mcuh.
> 
> Note that we can have a much simpler solution to this: disabling SSE4A
> on qemu64 completely, even on TCG. This way we can use PC_COMPAT_2_4
> instead of the kvm_default_props compat hack.
> 
> We can reenable SSE4A for TCG later (more exactly, we could enable
> everything from TCG_*_FEATURES) when we implement the kvm64/tcg64
> solution.
> 
> What do you think?

I would prefer that to this series.

Another possibility (even more of a hack, but perhaps acceptable) is to
disable SSE4A in x86_cpu_load_def if kvm_enabled() and the host vendor
is not AMD.  This is effectively what was already happening in 2.4 and
earlier.

Paolo