linux-kernel - Re: Linux with kvm-intel locks up VMplayer guest is started

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Message-ID: <48597735.50905@codemonkey.ws>
Date:	Wed, 18 Jun 2008 15:59:33 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Avi Kivity <avi@...ranet.com>
CC:	Martin Michlmayr <tbm@...ius.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Linux with kvm-intel locks up VMplayer guest is started

Avi Kivity wrote:
> Anthony Liguori wrote:
>>
>> We know exactly what the problem is.  KVM activates VT 
>> unconditionally.  There's no hardware mechanism to arbitrate access 
>> to VT.  KVM is the only thing in the Linux kernel that uses VT so we 
>> don't have a software mechanism to arbitrate access to VT.
>>
>> If the VMware code was upstream, then we could work together to make 
>> a software arbitration mechanism.  It's not, and worse yet, it's 
>> closed source so there's no chance it will be.  Even if someone wrote 
>> an arbitration mechanism and got VMware to use it, it still shouldn't 
>> be merged because KVM would be the only thing using that mechanism 
>> upstream.  I'm not interested in adding kernel infrastructure to 
>> support external binary kernel modules.
>
> Well a recent patch from Eli Collins mentioned VMware are 
> standardizing CR4.VMXE as an indicator of whether someone is using the 
> VT hardware or not, and now kvm clears that bit when unloading.  We 
> could check the bit and fail if is set, thus have working mutual 
> exclusion.  Of course, it will only work with newer versions of kvm 
> and vmware.

Yup, but the original bug reporter would not be helped by this.

> I don't see any reason to poke sticks into the wheels here.

An occasional poke at binary kernel modules is always a good thing IMHO :-)

Regards,

Anthony Liguori

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