Re: [PATCH v11 05/20] x86/virt/tdx: Add SEAMCALL infrastructure

[Dave Hansen]

On 6/7/23 11:53, Isaku Yamahata wrote:
>>> VMX enabling, and KVM is the only user of TDX.  This implementation
>>> chooses to make KVM itself responsible for enabling VMX before using
>>> TDX and let the rest of the kernel stay blissfully unaware of VMX.
>>>
>>> The current TDX_MODULE_CALL macro handles neither #GP nor #UD.  The
>>> kernel would hit Oops if SEAMCALL were mistakenly made w/o enabling VMX
>>> first.  Architecturally, there is no CPU flag to check whether the CPU
>>> is in VMX operation.  Also, if a BIOS were buggy, it could still report
>>> valid TDX private KeyIDs when TDX actually couldn't be enabled.
>> I'm not sure this is a great justification.  If the BIOS is lying to the
>> OS, we _should_ oops.
>>
>> How else can this happen other than silly kernel bugs.  It's OK to oops
>> in the face of silly kernel bugs.
> TDX KVM + reboot can hit #UD.  On reboot, VMX is disabled (VMXOFF) via
> syscore.shutdown callback.  However, guest TD can be still running to issue
> SEAMCALL resulting in #UD.
> 
> Or we can postpone the change and make the TDX KVM patch series carry a patch
> for it.

How does the existing KVM use of VMLAUNCH/VMRESUME avoid that problem?