linux-kernel - Re: [RFC][PATCH 0/2] x86: Add "virt flags"

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Message-ID: <20080908140939.GH11993@elte.hu>
Date:	Mon, 8 Sep 2008 16:09:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Sheng Yang <sheng.yang@...el.com>
Cc:	Avi Kivity <avi@...ranet.com>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 0/2] x86: Add "virt flags"


* Sheng Yang <sheng.yang@...el.com> wrote:

> Hi, Ingo
> 
> (sorry for former noises, I mistake the address... Report to lkml) 
> I've sent this patchset before, but got no comments from upstream at 
> that time.  So I'd like to resend this.
> 
> The virt flags is used for the important hardware virtualization 
> features, like EPT of incoming Nehalem. Because the feature 
> availability are read from MSRs, and I think virtualization features 
> should not at the same level as "vmx", so I added a new flags catagory 
> here.
> 
> But I still have concern, for this may broke some not that reliable 
> userspace programs. So Avi suggested that we can add more fields to 
> flags rather than a new catagory.  What's your opinion? We indeed need 
> a generic user visible way to tell the HW virtualization features.

hm, i think extending the already existing flags category sounds like a 
better solution than the separate virtual CPU flags line in 
/proc/cpuinfo. We already have self-invented flag entries (such as 
X86_FEATURE_NOPL), and adding more for virtualization would be quite 
natural to do, as long as it's reasonably close to the meaning of a 'CPU 
feature'.

Peter, what would be your preference?

	Ingo
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