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Message-ID: <6b425468-3aac-0123-c690-df8d750ce29e@suse.com>
Date: Mon, 17 Jul 2023 10:02:01 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: "Huang, Kai" <kai.huang@...el.com>,
"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
"peterz@...radead.org" <peterz@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: "Hansen, Dave" <dave.hansen@...el.com>,
"Christopherson,, Sean" <seanjc@...gle.com>,
"bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
"hpa@...or.com" <hpa@...or.com>,
"mingo@...hat.com" <mingo@...hat.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"Yamahata, Isaku" <isaku.yamahata@...el.com>,
"sathyanarayanan.kuppuswamy@...ux.intel.com"
<sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH 08/10] x86/tdx: Unify TDX_HYPERCALL and TDX_MODULE_CALL
assembly
On 17.07.23 г. 9:35 ч., Huang, Kai wrote:
>
>>> +/* Called from __tdx_hypercall() for unrecoverable failure */
>>> +static noinstr void __tdx_hypercall_failed(void)
>>> +{
>>> + instrumentation_begin();
>>> + panic("TDVMCALL failed. TDX module bug?");
>>> +}
>>
>> So what's the deal with this instrumentation here. The instruction is
>> noinstr, so you want to make just the panic call itself instrumentable?,
>> if so where's the instrumentation_end() cal;?No instrumentation_end()
>> call. Actually is this complexity really worth it for the failure case?
>>
>> AFAICS there is a single call site for __tdx_hypercall_failed so why
>> noot call panic() directly ?
>
> W/o this patch, the __tdx_hypercall_failed() is called from the TDX_HYPERCALL
> assembly, which is in .noinstr.text, and 'instrumentation_begin()' was needed to
> avoid the build warning I suppose.
>
> However now with this patch __tdx_hypercall_failed() is called from
> __tdx_hypercall() which is a C function w/o 'noinstr' annotation, thus I believe
> instrumentation_begin() and 'noinstr' annotation are not needed anymore.
>
> I didn't notice this while moving this function around and my kernel build test
> didn't warn me about this. I'll change in next version.
>
> In fact, perhaps this patch perhaps is too big for review. I will also try to
> split it to smaller ones.
Can't you simply call panic() directly? Less going around the code while
someone is reading it?
<snip>
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