Re: [RFC v2 14/32] x86/tdx: Handle port I/O

[Dave Hansen]

On 5/10/21 2:57 PM, Dan Williams wrote:
>> Decompression code uses port IO for earlyprintk. We must use
>> paravirt calls there too if we want to allow earlyprintk.
> What is the tradeoff between teaching the decompression code to handle
> #VE (the implied assumption) vs teaching it to avoid #VE with direct
> TDVMCALLs (the chosen direction)?

To me, the tradeoff is not just "teaching" the code to handle a #VE, but
ensuring that the entire architecture works.

Intentionally invoking a #VE is like making a function call that *MIGHT*
recurse on itself.  Sure, you can try to come up with a story about
bounding the recursion.  But, I don't see any semblance of that in this
series.

Exception-based recursion is really nasty because it's implicit, not
explicit.  That's why I'm advocating for a design where the kernel never
intentionally causes a #VE: it never intentionally recurses without bounds.