Re: [Xen-devel] Re: [RFC, PATCH 0/24] VMI i386 Linux virtualization interface proposal

[Anthony Liguori <aliguori@us.ibm.com>]

Zachary Amsden wrote:
> Chuck Ebbert wrote:
>> In-Reply-To: <20060315102522.GA5926@infradead.org>
>>
>> On Wed, 15 Mar 2006 10:25:22 +0000, Christoph Hellwig wrote:
>>   I'd like to see a test harness implementation that has no actual
>> hypervisor functionality and just implements the VMI calls natively.
>> This could be used to test the interface and would provide a nice
>> starting point for those who want to write a VMI hypervisor.
>>   
>
> I was going to make one yesterday.  But Fry's electronics stopped 
> carrying flashable blank PCI cards. :)  Anyone know of a vendor?
It's very practical to just patch Qemu to load a VMI rom as an option 
ROM.  That makes such an example VMI ROM very practical without having 
to build a special PCI device.

Regards,

Anthony Liguori
> It is possible to do in a software layer, although it really is a lot 
> easier to have the BIOS take care of all the fuss of finding a place 
> in low memory for you to live, setting up the various memory maps and 
> everything else for you.
>
> There is enormous benefit to having such a layer - you have a very 
> power test harness, not just to make sure VMI works, but even more 
> importantly, to inspect and verify the native kernel operation as 
> well.  You have a plethora of imporant hooks into the system, which 
> feed you knowledge you can not otherwise gain about which page tables 
> have been made active, when you take IRQs, where the kernel stack lives.
>
> All of this is ripe for a debug harness that can verify the kernel 
> doesn't overflow the kernel stack, doesn't write to active page table 
> entries without proper accessors and subsequent invalidations, and 
> obeys the rules that are required for correctness when running under a 
> hypervisor.  You probably even want to do hypervisor like things - 
> such as write protecting the kernel page tables so that you can be 
> confident there are no stray raw PTE accesses.
>
> We actually found one (harmless on native) in i386, which was enabling 
> NX bit.
>
> Zach
>
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