Re: x86info: dump kvm cpuid's

Re: x86info: dump kvm cpuid's

[Michael S. Tsirkin]

On Mon, Apr 30, 2012 at 11:43:19AM +0300, Gleb Natapov wrote:
> On Sun, Apr 29, 2012 at 01:10:21PM +0300, Michael S. Tsirkin wrote:
> > The following makes 'x86info -r' dump kvm cpu ids
> > (signature+features) when running in a vm.
> > 
> > On the guest we see the signature and the features:
> > eax in: 0x40000000, eax = 00000000 ebx = 4b4d564b ecx = 564b4d56 edx = 0000004d
> > eax in: 0x40000001, eax = 0100007b ebx = 00000000 ecx = 00000000 edx = 00000000
> > 
> > On the host it just adds a couple of zero lines:
> > eax in: 0x40000000, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > eax in: 0x40000001, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > 
> This is too KVM specific.

That's what I have. I scratch my own itch.

> Other hypervisors may use more cpuid leafs.

But not less so no harm's done.

> As far as I see Hyper-V uses 5 and use cpuid.0x40000000.eax as max cpuid
> leaf available. Haven't checked Xen or VMWare.

I don't think guessing at the CPU behaviour from linux source
is the right thing to do.

I Cc'd some addresses found in MAINTAINERS in the linux
kernel. This will give more people the opportunity
to ask for their stuff to be added, if they care.

> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > ---
> > 
> > Dave - not sure whether there's a mailing list for x86info.
> > The patch is on top of the master branch in
> > git://git.codemonkey.org.uk/x86info.git
> > 
> > Thanks!
> > 
> > diff --git a/x86info.c b/x86info.c
> > index 22c4734..dee5ed1 100644
> > --- a/x86info.c
> > +++ b/x86info.c
> > @@ -44,6 +44,7 @@ static void display_detailed_info(struct cpudata *cpu)
> >  
> >  		if (cpu->maxei2 >=0xC0000000)
> >  			dump_raw_cpuid(cpu->number, 0xC0000000, cpu->maxei2);
> > +		dump_raw_cpuid(cpu->number, 0x40000000, 0x40000001);
> >  	}
> >  
> >  	if (show_cacheinfo) {
> 
> --
> 			Gleb.

Re: x86info: dump kvm cpuid's

[Gleb Natapov]

On Mon, Apr 30, 2012 at 12:38:13PM +0300, Michael S. Tsirkin wrote:
> On Mon, Apr 30, 2012 at 11:43:19AM +0300, Gleb Natapov wrote:
> > On Sun, Apr 29, 2012 at 01:10:21PM +0300, Michael S. Tsirkin wrote:
> > > The following makes 'x86info -r' dump kvm cpu ids
> > > (signature+features) when running in a vm.
> > > 
> > > On the guest we see the signature and the features:
> > > eax in: 0x40000000, eax = 00000000 ebx = 4b4d564b ecx = 564b4d56 edx = 0000004d
> > > eax in: 0x40000001, eax = 0100007b ebx = 00000000 ecx = 00000000 edx = 00000000
> > > 
> > > On the host it just adds a couple of zero lines:
> > > eax in: 0x40000000, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > eax in: 0x40000001, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > 
> > This is too KVM specific.
> 
> That's what I have. I scratch my own itch.
> 
> > Other hypervisors may use more cpuid leafs.
> 
> But not less so no harm's done.
> 
> > As far as I see Hyper-V uses 5 and use cpuid.0x40000000.eax as max cpuid
> > leaf available. Haven't checked Xen or VMWare.
> 
> I don't think guessing at the CPU behaviour from linux source
> is the right thing to do.
> 
That is guessing from Hyper-V specification. The best kind of guess.

http://msdn.microsoft.com/en-us/library/windows/hardware/ff542700%28v=vs.85%29.aspx

> I Cc'd some addresses found in MAINTAINERS in the linux
> kernel. This will give more people the opportunity
> to ask for their stuff to be added, if they care.
> 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > 
> > > ---
> > > 
> > > Dave - not sure whether there's a mailing list for x86info.
> > > The patch is on top of the master branch in
> > > git://git.codemonkey.org.uk/x86info.git
> > > 
> > > Thanks!
> > > 
> > > diff --git a/x86info.c b/x86info.c
> > > index 22c4734..dee5ed1 100644
> > > --- a/x86info.c
> > > +++ b/x86info.c
> > > @@ -44,6 +44,7 @@ static void display_detailed_info(struct cpudata *cpu)
> > >  
> > >  		if (cpu->maxei2 >=0xC0000000)
> > >  			dump_raw_cpuid(cpu->number, 0xC0000000, cpu->maxei2);
> > > +		dump_raw_cpuid(cpu->number, 0x40000000, 0x40000001);
> > >  	}
> > >  
> > >  	if (show_cacheinfo) {
> > 
> > --
> > 			Gleb.

--
			Gleb.

Re: [Xen-devel] x86info: dump kvm cpuid's

[Ian Campbell]

On Mon, 2012-04-30 at 10:38 +0100, Michael S. Tsirkin wrote:
> On Mon, Apr 30, 2012 at 11:43:19AM +0300, Gleb Natapov wrote:
> > On Sun, Apr 29, 2012 at 01:10:21PM +0300, Michael S. Tsirkin wrote:
> > > The following makes 'x86info -r' dump kvm cpu ids
> > > (signature+features) when running in a vm.
> > > 
> > > On the guest we see the signature and the features:
> > > eax in: 0x40000000, eax = 00000000 ebx = 4b4d564b ecx = 564b4d56 edx = 0000004d
> > > eax in: 0x40000001, eax = 0100007b ebx = 00000000 ecx = 00000000 edx = 00000000
> > > 
> > > On the host it just adds a couple of zero lines:
> > > eax in: 0x40000000, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > eax in: 0x40000001, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > 
> > This is too KVM specific.
> 
> That's what I have. I scratch my own itch.
> 
> > Other hypervisors may use more cpuid leafs.
> 
> But not less so no harm's done.
> 
> > As far as I see Hyper-V uses 5 and use cpuid.0x40000000.eax as max cpuid
> > leaf available. Haven't checked Xen or VMWare.

Xen does the same, documentation in the Xen public interfaces header:
http://xenbits.xen.org/docs/unstable/hypercall/include,public,arch-x86,cpuid.h.html.

If compat mode for another h/v is enabled then those leaves will appear
at 0x40000000 and Xen's will be bumped up, so a fully Xen aware set of
drivers (or detection routine, etc) should check at 0x100 intervals
until 0x40010000 for the appropriate signatures (I realise that the docs
are somewhat lacking in this regard, I should cook up a patch).

Ian.

Re: [Xen-devel] x86info: dump kvm cpuid's

[Michael S. Tsirkin]

On Tue, May 01, 2012 at 11:29:04AM +0100, Ian Campbell wrote:
> On Mon, 2012-04-30 at 10:38 +0100, Michael S. Tsirkin wrote:
> > On Mon, Apr 30, 2012 at 11:43:19AM +0300, Gleb Natapov wrote:
> > > On Sun, Apr 29, 2012 at 01:10:21PM +0300, Michael S. Tsirkin wrote:
> > > > The following makes 'x86info -r' dump kvm cpu ids
> > > > (signature+features) when running in a vm.
> > > > 
> > > > On the guest we see the signature and the features:
> > > > eax in: 0x40000000, eax = 00000000 ebx = 4b4d564b ecx = 564b4d56 edx = 0000004d
> > > > eax in: 0x40000001, eax = 0100007b ebx = 00000000 ecx = 00000000 edx = 00000000
> > > > 
> > > > On the host it just adds a couple of zero lines:
> > > > eax in: 0x40000000, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > > eax in: 0x40000001, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > > 
> > > This is too KVM specific.
> > 
> > That's what I have. I scratch my own itch.
> > 
> > > Other hypervisors may use more cpuid leafs.
> > 
> > But not less so no harm's done.
> > 
> > > As far as I see Hyper-V uses 5 and use cpuid.0x40000000.eax as max cpuid
> > > leaf available. Haven't checked Xen or VMWare.
> 
> Xen does the same, documentation in the Xen public interfaces header:
> http://xenbits.xen.org/docs/unstable/hypercall/include,public,arch-x86,cpuid.h.html.

So ack to my patch?

> If compat mode for another h/v is enabled then those leaves will appear
> at 0x40000000 and Xen's will be bumped up, so a fully Xen aware set of
> drivers (or detection routine, etc) should check at 0x100 intervals
> until 0x40010000 for the appropriate signatures (I realise that the docs
> are somewhat lacking in this regard, I should cook up a patch).
> 
> Ian.

How does guest know that the data at 0x40000100 makes sense?

-- 
MST

Re: [Xen-devel] x86info: dump kvm cpuid's

[Ian Campbell]

On Tue, 2012-05-01 at 11:50 +0100, Michael S. Tsirkin wrote:
> On Tue, May 01, 2012 at 11:29:04AM +0100, Ian Campbell wrote:
> > On Mon, 2012-04-30 at 10:38 +0100, Michael S. Tsirkin wrote:
> > > On Mon, Apr 30, 2012 at 11:43:19AM +0300, Gleb Natapov wrote:
> > > > On Sun, Apr 29, 2012 at 01:10:21PM +0300, Michael S. Tsirkin wrote:
> > > > > The following makes 'x86info -r' dump kvm cpu ids
> > > > > (signature+features) when running in a vm.
> > > > > 
> > > > > On the guest we see the signature and the features:
> > > > > eax in: 0x40000000, eax = 00000000 ebx = 4b4d564b ecx = 564b4d56 edx = 0000004d
> > > > > eax in: 0x40000001, eax = 0100007b ebx = 00000000 ecx = 00000000 edx = 00000000
> > > > > 
> > > > > On the host it just adds a couple of zero lines:
> > > > > eax in: 0x40000000, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > > > eax in: 0x40000001, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000
> > > > > 
> > > > This is too KVM specific.
> > > 
> > > That's what I have. I scratch my own itch.
> > > 
> > > > Other hypervisors may use more cpuid leafs.
> > > 
> > > But not less so no harm's done.
> > > 
> > > > As far as I see Hyper-V uses 5 and use cpuid.0x40000000.eax as max cpuid
> > > > leaf available. Haven't checked Xen or VMWare.
> > 
> > Xen does the same, documentation in the Xen public interfaces header:
> > http://xenbits.xen.org/docs/unstable/hypercall/include,public,arch-x86,cpuid.h.html.
> 
> So ack to my patch?

I didn't see the patch, where should I be looking?

> > If compat mode for another h/v is enabled then those leaves will appear
> > at 0x40000000 and Xen's will be bumped up, so a fully Xen aware set of
> > drivers (or detection routine, etc) should check at 0x100 intervals
> > until 0x40010000 for the appropriate signatures (I realise that the docs
> > are somewhat lacking in this regard, I should cook up a patch).
> > 
> > Ian.
> 
> How does guest know that the data at 0x40000100 makes sense?

http://xenbits.xen.org/docs/unstable/hypercall/include,public,arch-x86,cpuid.h.html
EBX, ECX and EDX contain a signature "XenVMMXenVMM". I'm fairly certain
that hyperv has it's own magic number here.

Ian.