Re: [PATCH v9 04/18] x86/virt/tdx: Add skeleton to initialize TDX on demand

Dave Hansen
2023-02-14T17:23:57Z

On 2/14/23 04:46, Peter Zijlstra wrote:
> On Tue, Feb 14, 2023 at 12:59:11AM +1300, Kai Huang wrote:
>> Use a state machine protected by mutex to make sure the initialization
>> will only be done once, as tdx_enable() can be called multiple times
>> (i.e. KVM module can be reloaded) and be called concurrently by other
>> kernel components in the future.
> I still object to doing tdx_enable() at kvm module load.
>
> kvm.ko gets loaded unconditionally on boot, even if I then never use
> kvm.
>
> This stuff needs to be done when an actual VM is created, not before.

The actually implementation of this is hidden over in the KVM side of
this. But, tdx_enable() and all of this jazz should not be called on
kvm.ko load. It'll happen when the KVM tries to start the first TDX VM.

I think what Kai was thinking of was *this* sequence:

1. insmod kvm.ko
2. Start a TDX guest, tdx_enable() gets run
3. rmmod kvm
4. insmod kvm.ko (again)
5. Start another TDX guest, run tdx_enable() (again)

The rmmod/insmod pair is what triggers the second call of tdx_enable().