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From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
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Date: Wed, 26 Aug 2015 18:51:34 +0800
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Subject: Re: [Qemu-devel] [PATCH] target-i386: enable cflushopt/clwb/pcommit
	instructions
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: kvm@vger.kernel.org, mst@redhat.com, gleb@kernel.org, mtosatti@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, imammedo@redhat.com, pbonzini@redhat.com, rth@twiddle.net



On 08/22/2015 12:05 AM, Eduardo Habkost wrote:
> On Fri, Aug 21, 2015 at 01:05:12PM +0800, Xiao Guangrong wrote:
>> These instructions are used by NVDIMM drivers and the specification
>> locates at:
>> https://software.intel.com/sites/default/files/managed/0d/53/319433-022.pdf
>>
>> Let them be enabled on Broadwell on default
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>
> This breaks the ABI. If you change a CPU model you need machine compat
> code (see the TYPE_X86_CPU entries in PC_COMPAT_2_3 for example).
>
> And you can only change the CPU model in a new machine-type if that
> doesn't affect the runnability of a VM. In other words:
>
> If:
>    -machine pc-i440fx-2.4 -cpu <model>,enforcec
> is runnable in a given host, then
>    -machine pc-i440fx-2.5 -cpu <model>,enforce
> should be runnable too.
>

Eduardo, thanks for your info. I will dig into the code and fix this
issue in the next version.