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

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Message-ID: <m536wofeimei4wdronpl3xlr3ljcap3zazi3ffknpxzdfbrzsr@plk4veaz5d22>
Date: Thu, 18 Apr 2024 17:16:10 +0300
From: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: "seanjc@...gle.com" <seanjc@...gle.com>, 
	"Zhang, Tina" <tina.zhang@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>, 
	"Yuan, Hang" <hang.yuan@...el.com>, "x86@...nel.org" <x86@...nel.org>, 
	"Huang, Kai" <kai.huang@...el.com>, "Chen, Bo2" <chen.bo@...el.com>, 
	"sagis@...gle.com" <sagis@...gle.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "Aktas, Erdem" <erdemaktas@...gle.com>, 
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>, 
	"Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v19 007/130] x86/virt/tdx: Export SEAMCALL functions

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