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

kirill.shutemov
2024-04-18T14:16:15Z

On Tue, Apr 16, 2024 at 07:45:18PM +0000, Edgecombe, Rick P wrote:
> 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?

I converted all TDCALL and TDVMCALL leafs to direct assembly wrappers.
Here's WIP branch: https://github.com/intel/tdx/commits/guest-tdx-asm/

I still need to clean it up and write commit messages and comments for all
wrappers.

Now I think it worth the shot.

Any feedback?

--
Kiryl Shutsemau / Kirill A. Shutemov