linux-kernel - Re: [PATCH 1/2] VMware detection support for x86 and x86-64

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Message-ID: <20080917140357.GA23523@yantp.cn.ibm.com>
Date:	Wed, 17 Sep 2008 22:03:57 +0800
From:	Yan Li <elliot.li.tech@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Yan Li <elliot.li.tech@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	joerg.roedel@....com, rjmaomao@...il.com,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>, nancydreaming@...il.com
Subject: Re: [PATCH 1/2] VMware detection support for x86 and x86-64

On Wed, Sep 17, 2008 at 12:52:38PM +0200, Ingo Molnar wrote:
> > This code is from mtrr_trim_uncached_memory(), and used by
> > setup_arch(), which is used far before PCI is ready.
> > 
> > Therefore I think we can only use DMI here. Any idea?
> 
> PCI quirks can be used almost arbitrarily early stage, see:
> arch/x86/kernel/early-quirks.c.
> 
> Adding a VM identification callback to early-quirks.c would be fine. But 
> if there's a reliable and specific enough DMI string that's fine as 
> well. (but PCI is better, since it's a generally more stable enumeration 
> interface)

The problem here is that mtrr_trim_uncached_memory() is called 108
lines before the invocation of early_quirks(), and 48 lines before
that of dmi_scan_machine(). That's quite early.  The only thing ran
before that is the initialization of CPU, so we have nearly nothing to
use to check the fingerprint of the underlying machine.

I feel It's also unfit to touch the whole PCI or DMI thing before CPU
registers and memory are settled.  A simple solution here is to only
issue a KERN_INFO when we detected mtrr is empty and later, when we
can be sure that the OS is not running as a VM, issue a warning. The
later part can be done in early_quirks().

-- 
Li, Yan
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