Re: [RFC v1 00/26] Add TDX Guest Support

[Dave Hansen]

On 4/2/21 2:32 PM, Andi Kleen wrote:
>> If we go this route, what are the rules and restrictions?  Do we have to
>> say "no MMIO in #VE"?
> 
> All we have to say is "No MMIO in #VE before getting thd TDVEINFO arguments"
> After that it can nest without problems.

Well, not exactly.  You still can't do things that will could cause a n
unbounded recusive #VE.

It doesn't seem *that* far fetched to think that someone might try to
defer some work or dump data to the console.

> If you nest before that the TDX will cause a triple fault.
> 
> The code that cannot do it is a few lines in the early handler which
> runs with interrupts off.

>> Which brings up another related point: How do you debug TD guests?  Does
>> earlyprintk work?
> 
> Today it works actually because serial ports are allowed. But I expect it to
> be closed eventually because serial code is a lot of code to audit. 
> But you can always disable the filtering with a command line option and
> then it will always work for debugging.

Do we need a TDX-specific earlyprintk?  I would imagine it's pretty easy
to implement.