Re: [PATCH v7 6/6] x86/split_lock: Fix the split lock #AC handling when running as guest

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 10/14/2021 11:04 PM, Sean Christopherson wrote:
> On Thu, Oct 14, 2021, Xiaoyao Li wrote:
>> On 10/14/2021 5:32 AM, Sathyanarayanan Kuppuswamy wrote:
>>> + Xiaoyao
>>>
>>> On 10/13/21 1:30 PM, Sean Christopherson wrote:
>>>> On Tue, Oct 05, 2021, Kuppuswamy Sathyanarayanan wrote:
>>>>> From: Xiaoyao Li <xiaoyao.li@intel.com>
>>>>>
>>>>> If running as guest and hypervisor enables
>>>>> MSR_TEST_CTRL.SPLIT_LOCK_DETECT during its running, it can get split
>>>>> lock #AC even though sld_state is sld_off.
>>>> That's a hypervisor bug, no?  The hypervisor should never inject a fault
>>>> that the guest cannot reasonably expect.
>>
>> What if hypervisor doesn't intercept #AC and host enables SPLIT_LOCK_DETECT
>> during guest running? That's exactly the case TDX is facing.
> 
> That's a hypervisor bug.  Since it sounds like the TDX Module buries its head in
> the sand for split-lock #AC, KVM should refuse to run TDX guests if split-lock #AC
> is enabled.  Ideally the TDX Module would provide support for conditionally
> intercepting #AC, e.g. intercept and re-inject "normal" #AC, and exit to the VMM
> for split-lock #AC.  That would give VMMs the option of enabling split-lock
> detection in fatal mode for guests.
> 

We have bus lock VM exit for it.