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

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Date: Mon, 22 Apr 2024 12:50:31 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Rick P Edgecombe <rick.p.edgecombe@...el.com>
Cc: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>, Tina Zhang <tina.zhang@...el.com>, 
	Dave Hansen <dave.hansen@...el.com>, Hang Yuan <hang.yuan@...el.com>, 
	Kai Huang <kai.huang@...el.com>, "x86@...nel.org" <x86@...nel.org>, Bo2 Chen <chen.bo@...el.com>, 
	"sagis@...gle.com" <sagis@...gle.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Erdem Aktas <erdemaktas@...gle.com>, 
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	Isaku Yamahata <isaku.yamahata@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH v19 007/130] x86/virt/tdx: Export SEAMCALL functions

On Mon, Apr 22, 2024, Rick P Edgecombe wrote:
> On Mon, 2024-04-22 at 14:46 +0300, kirill.shutemov@...ux.intel.com wrote:
> > On Fri, Apr 19, 2024 at 08:04:26PM +0000, Edgecombe, Rick P wrote:
> > > On Fri, 2024-04-19 at 17:46 +0300, kirill.shutemov@...ux.intel.com wrote:
> > > > 
> > > > > Side topic #3, the ud2 to induce panic should be out-of-line.
> > > > 
> > > > Yeah. I switched to the inline one while debugging one section mismatch
> > > > issue and forgot to switch back.
> > > 
> > > Sorry, why do we need to panic?
> > 
> > It panics in cases that should never occur if the TDX module is
> > functioning properly. For example, TDVMCALL itself should never fail,
> > although the leaf function could.
> 
> Panic should normally be for desperate situations when horrible things will
> likely happen if we continue, right? Why are we adding a panic when we didn't
> have one before? Is it a second change, or a side affect of the refactor?

The kernel already does panic() if TDCALL itself fails,

  static inline void tdcall(u64 fn, struct tdx_module_args *args)
  {
	if (__tdcall_ret(fn, args))
		panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
  }

  /* Called from __tdx_hypercall() for unrecoverable failure */
  noinstr void __noreturn __tdx_hypercall_failed(void)
  {
	instrumentation_begin();
	panic("TDVMCALL failed. TDX module bug?");
  }

it's just doesn in C code via panic(), not in asm via a bare ud2.