From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCHv2] x86info: dump kvm cpuid's
Date: Wed, 2 May 2012 12:50:55 +0300
Message-ID: <20120502095053.GA31543@redhat.com>
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To: Ian Campbell <ijc@hellion.org.uk>
Cc: xen-devel@lists.xensource.com, kvm@vger.kernel.org, pv-drivers@vmware.com, virtualization@lists.linux-foundation.org, devel@linuxdriverproject.org, davej@redhat.com
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On Wed, May 02, 2012 at 10:45:27AM +0100, Ian Campbell wrote:
> On Tue, 2012-05-01 at 16:04 +0300, Gleb Natapov wrote:
> > > BTW, according to arch/x86/include/asm/kvm_para.h unsurprisingly KVM has
> > > a signature too 'KVMKVMKVM'.
> > > 
> > > >  	cpu->stepping = eax & 0xf;
> > > >  	cpu->model = (eax >> 4) & 0xf;
> > > >  	cpu->family = (eax >> 8) & 0xf;
> > > > @@ -29,6 +29,19 @@ void get_cpu_info_basics(struct cpudata *cpu)
> > > >  
> > > >  	cpuid(cpu->number, 0xC0000000, &maxei, NULL, NULL, NULL);
> > > >  	cpu->maxei2 = maxei;
> > > > +	if (ecx & 0x80000000) {
> > > > +		cpuid(cpu->number, 0x40000000, &maxhv, NULL, NULL, NULL);
> > > > +		/*
> > > > +		 * KVM up to linux 3.4 reports 0 as the max hypervisor leaf,
> > > > +		 * where it really means 0x40000001.
> > > 
> > > This is something where I definitely think you want to check the
> > > signature first.
> > In theory yes, but in practice what will this break?
> 
> I've got no idea -- but what's the harm in checking?
> 
> Ian.

Users can set kvm signature to anything, if they do
debugging will be a bit harder for them.

> -- 
> Ian Campbell
> Current Noise: Hypocrisy - Roswell 47
> 
> Angels we have heard on High
> Tell us to go out and Buy.
> 		-- Tom Lehrer