linux-kernel - Re: cpuinfo and HVM features

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Date:	Mon, 27 Jul 2009 13:31:07 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
CC:	"Yang, Sheng" <sheng.yang@...el.com>,
	"H. Peter Anvin" <h.peter.anvin@...el.com>,
	Gregory Haskins <gregory.haskins@...il.com>,
	kvm-devel <kvm@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: cpuinfo and HVM features

On 07/27/2009 12:08 PM, Jan Kiszka wrote:
>> When I add feature reporting to cpuinfo, I just put highlight features there,
>> otherwise the VMX feature list would at least as long as CPU one.
>>      
>
> That could become true. But the question is always what the highlights
> are. Often this depends on the hypervisor as it may implement
> workarounds for missing features differently (or not at all). So I'm
> also for exposing feature information consistently.
>    


I'd put everything in there.  It's information that is often useful.  
Even minor features can expose bugs in the hypervisor.

>> I have also suggested another field for virtualization feature for it, but
>> some concern again userspace tools raised.
>>
>> For we got indeed quite a lot features, and would get more, would it better to
>> export the part of struct vmcs_config entries(that's pin_based_exec_ctrl,
>> cpu_based_exec_ctrl, and cpu_based_2nd_exec_ctrl) through
>> sys/module/kvm_intel/? Put every feature to cpuinfo seems not that necessary
>> for such a big list.
>>      
>
> I don't think this information should only come from KVM. Consider you
> didn't build it into some kernel but still want to find out what your
> system is able to provide.
>
> What about adding some dedicated /proc entry for CPU virtualization
> features, say /proc/hvminfo?
>    

The flags line is already very long, and already has some virt features, 
so I see no problem extending it.  If we don't want that. I'd prefer a 
virtualization  line in /proc/cpuinfo rather than a new file.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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