Re: [PATCH v19 007/130] x86/virt/tdx: Export SEAMCALL functions

Edgecombe, Rick P
2024-04-16T19:45:24Z

On Wed, 2024-04-10 at 15:49 +0300, Kirill A. Shutemov wrote:
> On Fri, Mar 15, 2024 at 09:33:20AM -0700, Sean Christopherson wrote:
> > So my feedback is to not worry about the exports, and instead focus on
> > figuring
> > out a way to make the generated code less bloated and easier to read/debug.
>
> I think it was mistake trying to centralize TDCALL/SEAMCALL calls into
> few megawrappers. I think we can get better results by shifting leaf
> function wrappers into assembly.
>
> We are going to have more assembly, but it should produce better result.
> Adding macros can help to write such wrapper and minimizer boilerplate.
>
> Below is an example of how it can look like. It's not complete. I only
> converted TDCALLs, but TDVMCALLs or SEAMCALLs. TDVMCALLs are going to be
> more complex.
>
> Any opinions? Is it something worth investing more time?

We discussed offline how implementing these for each TDVM/SEAMCALL increases the
chances of a bug in just one TDVM/SEAMCALL. Which could making debugging
problems more challenging. Kirill raised the possibility of some code generating
solution like cpufeatures.h, that could take a spec and generate correct calls.

So far no big wins have presented themselves. Kirill, do we think the path to
move the messy part out-of-line will not work?