Re: [patch] VMX Unrestricted mode support

Avi Kivity
2009-05-31T16:01:06Z

Anthony Liguori wrote:
> Nitin A Kamble wrote:
>
>> Avi,
>>
>> A new VMX feature "Unrestricted Guest" feature is added in the VMX
>> specification. You can look at the latest Intel processor manual for
>> details of the feature here:
>>
>> http://www.intel.com/products/processor/manuals
>>
>> It allows kvm guests to run real mode and unpaged mode
>> code natively in the VMX mode when EPT is turned on. With the
>> unrestricted guest there is no need to emulate the guest real mode code
>> in the vm86 container or in the emulator. Also the guest big real mode
>> code works like native.
>>
>> The attached patch enhances KVM to use the unrestricted guest feature
>> if available on the processor. It also adds a new kernel/module
>> parameter to disable the unrestricted guest feature at the boot time.
>>
>> Signed-Off-By: Nitin A Kamble <nitin.a.kamble@intel.com>
>>
>> Thanks & Regards,
>> Nitin
>>
>>
>
> It may make sense to expose this as a CAP down to userspace.
>
> We could possibly make better error messages in userspace when we get an
> unknown vmexit failure on pre-wsm hardware.
>

If we see the dreaded 0x80000021 and CR0.PE=0, then we're likely seeing
a real mode emulation problem.

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error compiling committee.c: too many arguments to function