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

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Date: Tue, 23 Apr 2024 00:28:02 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
CC: "Zhang, Tina" <tina.zhang@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Huang, Kai"
	<kai.huang@...el.com>, "x86@...nel.org" <x86@...nel.org>, "Chen, Bo2"
	<chen.bo@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>, "Aktas,
 Erdem" <erdemaktas@...gle.com>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>
Subject: Re: [PATCH v19 007/130] x86/virt/tdx: Export SEAMCALL functions

On Mon, 2024-04-22 at 12:50 -0700, Sean Christopherson wrote:
> 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.

Hmm, I didn't realize. It looks like today some calls do and some don't. I don't
mean to reopen old debates. Just surprised that these are able to bring down the
system. Which funnily enough connects back to the original issue of the patch:
whether they are safe to export for module use.