Re: [PATCH] KVM: VMX: Inform user about INTEL_TXT dependency

[Jan Kiszka <jan.kiszka@web.de>]

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Am 14.11.2010 11:30, Avi Kivity wrote:
> On 11/14/2010 11:18 AM, Jan Kiszka wrote:
>> From: Jan Kiszka<jan.kiszka@siemens.com>
>>
>> Without CONFIG_INTEL_TXT, the user must not enable this feature in the
>> BIOS. Otherwise, KVM will not work. Explain this dependency via a kernel
>> log message.
>>
>> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>> ---
>>   arch/x86/kvm/vmx.c |    7 ++++++-
>>   1 files changed, 6 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 9367abc..ebafd57 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -1306,8 +1306,13 @@ static __init int vmx_disabled_by_bios(void)
>>               &&  tboot_enabled())
>>               return 1;
>>           if (!(msr&  FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX)
>> -            &&  !tboot_enabled())
>> +            &&  !tboot_enabled()) {
>> +#ifndef CONFIG_INTEL_TXT
>> +            printk(KERN_INFO "kvm: if TXT is enabled in the bios, "
>> +                     "kvm depends on CONFIG_INTEL_TXT\n");
>> +#endif
>>               return 1;
>> +        }
>>       }
>>
> 
> Maybe reword to an instruction?
> 
> Something like
> 
>   kvm: TXT enabled in the bios.  Either disable TXT in the bios, or
> enable CONFIG_INTEL_TXT in your kernel.
> 

I always get an aching head when thinking about these dependency: Does
FEATURE_CONTROL_LOCKED && !FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX
imply that the BIOS uses TXT? Or could it also mean that it just
disabled VT-x explicitly? As CONFIG_INTEL_TXT is off, we do not know if
tboot_enabled is off as well.

Jan


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