Re: [Qemu-devel] [PATCH] target-i386: upgrade family number of qemu64 CPU model to 15

[Eduardo Habkost]

On Thu, Apr 18, 2013 at 02:47:21PM +0000, Ren, Yongjie wrote:
> > -----Original Message-----
> > From: Gleb Natapov [mailto:address@hidden
> > Sent: Thursday, April 18, 2013 7:08 PM
> > To: Ren, Yongjie
> > Cc: Marcelo Tosatti; address@hidden; address@hidden;
> > address@hidden
> > Subject: Re: [PATCH] target-i386: upgrade family number of qemu64 CPU
> > model to 15
> > 
> > On Thu, Apr 18, 2013 at 10:45:38AM +0000, Ren, Yongjie wrote:
> > > qemu64 is the default CPU model for QEMU/KVM on x86-64, but its
> > family number
> > > definition is not accurate. The vendor of 'qemu64' is defined as 'AMD'.
> > For AMD
> > > processors, AMD K8 (i.e. Family 15) firstly introduced SSE3 instruction
> > set.
> > > 'qemu64' already has 'CPUID_EXT_SSE3' in its ext_features, but its family
> > > number is only 6 which is not equal to or greater than 15.
> > > So, upgrade the CPU family number of qemu64 model to 15.
> > > After this upgrade, 32bit Windows 8 can boot up with qemu64 CPU
> > model.
> > > This upgrade can be also a fix to the below bug about 32bit Windows 8
> > booting.
> > > https://bugs.launchpad.net/qemu/+bug/1007269
> > 
> > Changing cpuid info is not that simple since this is guest visible
> > information and can impact migration. Old machine models should still
> > expose the old family.
> > 
> Sorry, I didn't consider migration issue. I just think the cupid info for 
> qemu64
> is not compatible with real-world CPU. Family 6 AMD CPU should not have
> SSE3 but it has SSE3 in qemu64 model.
> If it's not so simple to modify cupid info, just ignore my patch.  :-)

We have other fixes for CPUID information sent by other people that will
require special handling to allow migration compatibility as well.

The ongoing static-properties and X86CPU subclasses work would help us
on this, but they probably won't be in 1.5. So I am planning to gather
those CPUID fixes and make them use a simple (and temporary)
compatibility mechanism and submit them next week.

-- 
Eduardo