Re: [PATCH 09/21] KVM: TDX: Retry seamcall when TDX_OPERAND_BUSY with operand SEPT

[Edgecombe, Rick P]

On Tue, 2024-10-15 at 12:03 +1300, Huang, Kai wrote:
> > "Is going to", as in "will be changed to"? Or "does today"?
> 
> Will be changed to (today's behaviour is to go back to guest to let the 
> fault happen again to retry).
> 
> AFAICT this is what Sean suggested:
> 
> https://lore.kernel.org/all/ZuR09EqzU1WbQYGd@xxxxxxxxxx/
> 
> The whole point is to let KVM loop internally but not go back to guest 
> when the fault handler sees a frozen PTE.  And in this proposal this 
> applies to both leaf and non-leaf PTEs IIUC, so it should handle the 
> case where try_cmpxchg64() fails as mentioned by Yan.
> 
> > 
> > > retry internally for
> > > step 4 (retries N times) because it sees the frozen PTE, but will never go
> > > back
> > > to guest after the fault is resolved?  How can step 4 triggers zero-step?
> > 
> > Step 3-4 is saying it will go back to the guest and fault again.
> 
> As said above, the whole point is to make KVM loop internally when it 
> sees a frozen PTE, but not go back to guest.

Yea, I was saying on that idea that I thought looping forever without checking
for a signal would be problematic. Then userspace could re-enter the TD. I don't
know if it's a show stopper.

In any case the discussion between these threads and LPC/KVM forum hallway
chatter has gotten a bit fragmented. I don't think there is any concrete
consensus solution at this point.