Re: [PATCH v8 12/16] x86/virt/tdx: Designate the global KeyID and configure the TDX module

[Dave Hansen]

On 1/10/23 02:48, Huang, Kai wrote:
>>>
>>> +   /*
>>> +    * Use the first private KeyID as the global KeyID, and pass
>>> +    * it along with the TDMRs to the TDX module.
>>> +    */
>>> +   ret = config_tdx_module(&tdmr_list, tdx_keyid_start);
>>> +   if (ret)
>>> +           goto out_free_pamts;
>> This is "consuming" tdx_keyid_start.  Does it need to get incremented
>> since the first guest can't use this KeyID now?
> 
> It depends on how we treat 'tdx_keyid_start'.  If it means the first _usable_
> KeyID for KVM, then we should increase it; but if it only used for the hardware-
> enabled TDX KeyID range, then we don't need to increase it.
> 
> Currently it is marked as __ro_after_init so my intention is the latter (also in
> the spirit of keeping this series minimal).
> 
> Eventually we will need to have functions to allocate/free TDX KeyIDs anyway for
> KVM, but in that we can just treat 'tdx_keyid_start + 1' as the first usable
> KeyID.

So, basically, you're going to depend on the KVM code (which isn't in
this series) to magically know exactly what this series did?  Then,
you're expecting that this code will never change in a way that breaks
this random KVM code?

That's frankly awful.

Make the variable read/write.  Call it tdx_guest_keyid_start, and
increment it when you make a keyid unavailable for guest use.